In IBAHCM/RPiR: Reproducible Programming in R
knitr::opts_chunk$set(echo = TRUE)
This page explains how to debug your code. There are many ways in which this
can be done, so we've split them into levels ranging from basic to more
advanced methods. First though:
Don't ignore warnings!
People often put statements into their code to reduce the number of warnings it
generates to make it look prettier. This is always a terrible idea, as if new
warnings are introduced by a mistake, you won't see them (because you suppressed
them!), so please don't do any of the following:
suppressWarnings()
suppressPackageStartupMessages()
library(dplyr, warn.conflicts = FALSE)
Or anything else like that. We will never mark you down for generating warning
messages in your code (unless they are real warnings about real problems in
your code of course!).
Restart R and never save .RData files
Errors can often be transitory because of something weird in your current
environment, and while that's not great it's just not worth worrying too much
about, so it's always worth restarting R and trying again before you
panic and try debugging the problem, which can take a while.
However, if you save and restore .RData files, then when you restart R you won't
delete all of the mistakes you made in the last R session - the objects present
in the last session will still be there after restarting - and your code will
no longer be reproducible. As a result we strongly encourage you to never save
or restore these files. To disable this, open the (global) preferences in
RStudio, and untick "Restore .RData into workspace at startup" and set "Save
workspace to .RData on exit:" to "Never".
knitr::include_graphics('images/debugging.png')
Once you've not ignoring the error messages, and you've tried restarting R and
it hasn't helped, then you need to try debugging the code for real, we're
afraid. Here's an approach you could try:
Watch the video on debugging
This would be a good time to watch this keynote from
rstudio::conf 2020 by Jenny Bryan. It is an excellent keynote on errors in
R and how to identify and fix them.
Level 1 - Check for typos
Read the error or warning message carefully and try to decipher it.
- Have you seen it before?
- Are there any recognizable function or object names that might give you a clue
as to what is causing the error?
- Are there any spelling mistakes in your code that might be causing a problem?
Check the names of your functions, arguments, and objects.
- Does your function transform an object that is neither created earlier in the
function nor passed as an argument?
- Do you have mismatching brackets, missing commas, or other strange symbols
that shouldn't be there?
- Have you tried doing an internet search? If you're lucky, someone else might
have had a similar problem and posted on Stack Overflow.
Level 2 - Tracking the error
If the problem is not immediately obvious from the error statement or a search
for typos, you try running through the code line by line, or inserting
print() statements.
If your code / function is short, it can be helpful to run the code line by
line, viewing constructed objects as you go and confirming they match what is
expected. This can be done by highlighting individual objects or lines of code
and pressing Command + Enter on a Mac (Ctrl + Enter on Windows).
If your code is more complex -- if you have a number of functions that call on
each other for example -- then running your code line by line might be too
confusing. In this case you might want to try inserting print() or str()
statements at key points in your code. This is especially useful if you have
some idea where the error is occurring! This can be done by calling
traceback() immediately after an error occurs.
a <- function(x) x + y
b <- function(x) a(x)
b(2)
traceback()
This function prints a list of functions (calls) that have lead to the error
being triggered. This list is called the call stack (or stack trace).
Level 3 - Browsing the error
sfsdf
Examples
For each problem, try copying the code into an instance of RStudio and work
from there. Accompanying solutions are provided in a separate tab.
Error: could not find function {.tabset}
Problem
Define a calculate() function, which calls add2() and multiplyby8() to
perform the following calculation:
$$y = 8(x + 2)$$
multiplyby8 <- function(value) {
value * 8
}
add2 <- function(value) {
result <- value + 2
multiplby8(result)
}
calculate <- function(value) {
add2(value)
}
calculate(2)
Hints
In this problem, R couldn't find the function multiplby8():
The function calculate() calls add2(), which itself calls multiplby8(),
which doesn't exist!
Solution
multiplyby8 <- function(value) {
value * 8
}
add2 <- function(value) {
result <- value + 2
multiplyby8(result) # fix the typo here!
}
calculate <- function(value) {
add2(value)
}
calculate(2)
{-}
Error: Unexpected '}' in {.tabset}
Problem
The cats() function determines cat vocalisations based on their age.
cats <- data.frame(name = c("Cady", "Kitten", "Cleo"),
age = c(15, 14, 3))
for (i in 1:3) {
cat <- cats[i, ]
if (cat$age > 10) {
for (j in seq_len(cat$age)) {
meows <- rep("Meeooooww!", cat$age)
}
}
msg <- paste(cat$name, "Meeooooww!")
}
} else {
msg <- paste(cat$name, "Pew! Pew!")
}
print(msg)
}
Hints
There are too many brackets here. It's easier to see which opening and closing
brackets match by highlighting the lines (or pressing Command + A on a Mac
/ Ctrl + A on Windows), then using the Reindent Lines shortcut (in the menu
bar, select Code, then Reindent Lines; or pressing Command + I on a Mac /
Ctrl + I on Windows).
There are two extra curly brackets on lines 10 and 12.
To make the code easier to read, even more curly brackets can be removed.
Since both the contents of the for loop and the contents of the else
statement comprise only a single line.
Solution
cats <- data.frame(name = c("Cady", "Kitten", "Cleo"),
age = c(15, 14, 3))
for (i in 1:3) {
cat <- cats[i, ]
if (cat$age > 10) {
for (j in seq_len(cat$age))
meows <- rep("Meeooooww!", cat$age)
msg <- paste(cat$name, "Meeooooww!")
} else
msg <- paste(cat$name, "Pew! Pew!")
print(msg)
}
{-}
Error: unexpected '=' in {.tabset}
Problem
Define a countdown() function, which counts down from a number before
printing "Blast off!" to the console.
countdown <- function(number) {
if (number < 0) {
stop("Can't countdown from a negative time.")
} else {
timestep <- number
for (i in 1:number) {
print(timestep)
timestep <- timestep - 1
Sys.sleep(1)
if (timestep = 0)
print("Blast off!")
}
}
}
countdown(3)
Hints
As the error stated, R has found an unexpected =:
Here, the code stops after hitting the first error. That's because of the way
this website is generated. In RStudio, a number of unexpected '}' in ...
errors follow this. The number of errors here might seem intimidating, but the
important thing to note is that after we fix the first one, the remaining three
will cease to occur. It's very important, therefore, to tackle errors in
sequence.
So, returning to the unexpected =... the only = can be found on line 19.
Now, recall that if statements are always followed by a condition. That is,
a conditional test that results in TRUE or FALSE.
Solution
countdown <- function(number) {
if (number < 0) {
stop("Can't countdown from a negative time.")
} else {
timestep <- number
for (i in 1:number) {
print(timestep)
timestep <- timestep - 1
Sys.sleep(1)
if (timestep == 0) # fix conditional test
print("Blast off!")
}
}
}
countdown(3)
{-}
Error: object not found {.tabset}
Problem
Given an acceleration from a point of rest and a time of travel, calculate
the displacement of an object using Newton's second equation of
motion:
$$s = ut + \frac{1}{2}at^2$$
displacement <- function(acceleration, time) {
starting_speed <- 0
initial_velocity * time + (0.5 * acceleration * (time ^ 2))
}
displacement(10, 18)
Hints
Here, an error is generated on line 3 when R tries to multiply
initial_velocity by time, but can't find an initial_velocity object:
If an object is not defined earlier in the function, then it must be passed as
an argument. It can't just magically appear out of thin air!
Solution
displacement <- function(acceleration, time) {
initial_velocity <- 0 # initialise the object here!
initial_velocity * time + (0.5 * acceleration * (time ^ 2))
}
displacement(10, 18)
{-}
Error: missing value where TRUE/FALSE needed {.tabset}
Problem
The checker() function checks whether a number is big (greater than 10) or
small (less than or equal to 10) and prints out a descriptive statement to the
console.
checker <- function(value) {
if (value > 10) {
print("Big number")
} else {
print("Small number")
}
}
items <- list(2, 8, NA, 32)
for (i in items) {
checker(i)
}
Hints
Here, R is returning an error on the third iteration of the for loop:
There if an error in if (value > 10) because a TRUE/FALSE value is expected.
In this case, checker() is trying to determine whether the value, NA, is
greater than 10. Since NA > 10 returns NA and if else statements only
accept boolean values, an error is generated.
Solution
The solution here is to either remove NA from the items vector or check for
non-numeric values in the function.
checker <- function(value) {
if (!is.numeric(value)) { # check for
print("Not a number") # non-numeric
} else if (value > 10) { # values here!
print("Big number")
} else {
print("Small number")
}
}
items <- list(2, 8, NA, 32)
for (i in items) {
checker(i)
}
{-}
Warning: the condition has length > 1 and only the first element will be used {.tabset}
Problem
The function explode() takes a number between 0 and 11, otherwise NA is
returned. Values between 0 and 10 are incremented by 1, whereas 11 is reset
to 0.
explode <- function(value) {
if (value > 11) {
output <- NA
} else if (value == 11) {
output <- 0
} else {
output <- value + 1
}
output
}
vector <- c(2, 4, 11, 27, 15)
explode(vector)
Hints
Here we have a warning that has been triggered by if (value > 11). In this
case, it's particularly dangerous because a Warning doesn't stop your code
like an Error does, and here, erroneous values are returned!
The warnings are triggered on lines 3 and 7, where vector (a five element
vector) is passed into explode() as the value argument.
The problem is that the condition (if (condition)) must have a length of 1
and therefore only the first element of the vector is being used in the
comparison. That is, value is input as c(2, 4, 11, 27, 15), but the
condition value > 11 tests on 2, returning FALSE. Then the condition
value == 11 tests on 2, again returning FALSE. So then output <- value + 1
returns c(3, 5, 12, 28, 16).
Solution
The solution here is to either (1) ensure the function can only take a single
input value; or (2) wrap the if else statements in a for loop, so that
each element of the vector can be checked and transformed individually. Here
we do the former:
explode <- function(value) {
if (length(value) > 1) # add a check
stop("Input must be a single value") # here
if (value > 11) {
output <- NA
} else if (value == 11) {
output <- 0
} else {
output <- value + 1
}
output
}
vector <- c(2, 4, 11, 27, 15)
for (i in vector) { # and loop
explode(i) # through the
} # vector here
{-}
Error: unexpected symbol in {.tabset}
Problem
The quadratic() function is used to solve quadratic equations.
quadratic <- function(a, b, c) {
root <- sqrt(b^2 - 4ac)
solution1 <- -b + root / 2a
solution2 <- -b - root / 2a
list(solution1 solution2)
}
quadratic(1, -5, 6)
Hints
An unexpected symbol can often be avoided by keeping good code hygiene and
making sure everything is neat and tidy. A good way to do this is to make
good use of white space (blank lines between sections of code) as well as
making a habit of selecting all of your code (Command + A on Mac /
Ctrl + A on Windows), then reindenting your lines (Command + I on Mac /
Ctrl + I on Windows).
In this case, that won't help because each error occurs on a single line. There
are 4 syntax errors -- errors in the grammar of code -- in total, see if you
can find them all.
Solution
quadratic <- function(a, b, c) {
root <- sqrt(b^2 - 4 * a * c) # here,
solution1 <- -b + root / 2 * a # here,
solution2 <- -b - root / 2 * a # here,
list(solution1, solution2) # and here!
}
quadratic(1, -5, 6)
{-}
Error: replacement has, data has {.tabset}
Problem
There are no functions here. We only wish to add a new column to a dataframe.
data <- data.frame(colour = c("teal", "mustard yellow", "leaf green", "dark",
"candyfloss pink", "quite a nice brown"),
number = c(3328476, 9832, 23992611, 213987, 487621, 6328974))
data$time <- seq(0, 9, 2)
Hints
This error is a little difficult to read:
The key point to note here is that the replacement has 5 rows but the data
has 6... and the replacement here is time.
Solution
data <- data.frame(colour = c("teal", "mustard yellow", "leaf green", "dark",
"candyfloss pink", "quite a nice brown"),
number = c(3328476, 9832, 23992611, 213987, 487621, 6328974))
data$time <- seq(0, 9, 1.67)
{-}
Error: object of type 'closure' is not subsettable {.tabset}
Problem
The force() function calculates Newton's second law of motion.
force <- function(mass, acceleration) {
mass * acceleration
}
dat <- data.frame(mass = c(20, 23, 27), acceleration = c(30, 40, 62))
for (i in seq_len(nrow(dat))) {
mean[i] <- force(dat$mass[i], dat$acceleration[i])
}
mean
Hints
This is a tricky one that might require an internet search (for Stack
Overflow) to solve.
Reading the error message, we know that the error is
triggered on line 11 by mean[i] <- force(dat$mass[i], dat$acceleration[i]):
The problem is that "object of type 'closure' is not subsettable". What does
this mean?
Solution
force <- function(mass, acceleration) {
mass * acceleration
}
dat <- data.frame(mass = c(20, 23, 27), acceleration = c(30, 40, 62))
results <- c() # define results object first and don't give an object
# the same name as a function!
for (i in seq_len(nrow(dat))) {
results[i] <- force(dat$mass[i], dat$acceleration[i])
}
results
{-}
IBAHCM/RPiR documentation built on Jan. 12, 2023, 7:41 p.m.
R Package Documentation
Browse R Packages
We want your feedback!
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knitr::opts_chunk$set(echo = TRUE)
This page explains how to debug your code. There are many ways in which this can be done, so we've split them into levels ranging from basic to more advanced methods. First though:
Don't ignore warnings!
People often put statements into their code to reduce the number of warnings it generates to make it look prettier. This is always a terrible idea, as if new warnings are introduced by a mistake, you won't see them (because you suppressed them!), so please don't do any of the following:
suppressWarnings() suppressPackageStartupMessages() library(dplyr, warn.conflicts = FALSE)
Or anything else like that. We will never mark you down for generating warning messages in your code (unless they are real warnings about real problems in your code of course!).
Restart R and never save .RData files
Errors can often be transitory because of something weird in your current environment, and while that's not great it's just not worth worrying too much about, so it's always worth restarting R and trying again before you panic and try debugging the problem, which can take a while.
However, if you save and restore .RData files, then when you restart R you won't
delete all of the mistakes you made in the last R session - the objects present
in the last session will still be there after restarting - and your code will
no longer be reproducible. As a result we strongly encourage you to never save
or restore these files. To disable this, open the (global) preferences in
RStudio, and untick "Restore .RData into workspace at startup" and set "Save
workspace to .RData on exit:" to "Never".
knitr::include_graphics('images/debugging.png')
Once you've not ignoring the error messages, and you've tried restarting R and it hasn't helped, then you need to try debugging the code for real, we're afraid. Here's an approach you could try:
Watch the video on debugging
This would be a good time to watch this keynote from rstudio::conf 2020 by Jenny Bryan. It is an excellent keynote on errors in R and how to identify and fix them.
Level 1 - Check for typos
Read the error or warning message carefully and try to decipher it.
- Have you seen it before?
- Are there any recognizable function or object names that might give you a clue as to what is causing the error?
- Are there any spelling mistakes in your code that might be causing a problem? Check the names of your functions, arguments, and objects.
- Does your function transform an object that is neither created earlier in the function nor passed as an argument?
- Do you have mismatching brackets, missing commas, or other strange symbols that shouldn't be there?
- Have you tried doing an internet search? If you're lucky, someone else might have had a similar problem and posted on Stack Overflow.
Level 2 - Tracking the error
If the problem is not immediately obvious from the error statement or a search
for typos, you try running through the code line by line, or inserting
print() statements.
If your code / function is short, it can be helpful to run the code line by
line, viewing constructed objects as you go and confirming they match what is
expected. This can be done by highlighting individual objects or lines of code
and pressing Command + Enter on a Mac (Ctrl + Enter on Windows).
If your code is more complex -- if you have a number of functions that call on
each other for example -- then running your code line by line might be too
confusing. In this case you might want to try inserting print() or str()
statements at key points in your code. This is especially useful if you have
some idea where the error is occurring! This can be done by calling
traceback() immediately after an error occurs.
a <- function(x) x + y b <- function(x) a(x) b(2) traceback()
This function prints a list of functions (calls) that have lead to the error being triggered. This list is called the call stack (or stack trace).
Level 3 - Browsing the error
sfsdf
Examples
For each problem, try copying the code into an instance of RStudio and work from there. Accompanying solutions are provided in a separate tab.
Error: could not find function {.tabset}
Problem
Define a calculate() function, which calls add2() and multiplyby8() to
perform the following calculation:
$$y = 8(x + 2)$$
multiplyby8 <- function(value) { value * 8 } add2 <- function(value) { result <- value + 2 multiplby8(result) } calculate <- function(value) { add2(value) } calculate(2)
Hints
In this problem, R couldn't find the function multiplby8():
The function calculate() calls add2(), which itself calls multiplby8(),
which doesn't exist!
Solution
multiplyby8 <- function(value) { value * 8 } add2 <- function(value) { result <- value + 2 multiplyby8(result) # fix the typo here! } calculate <- function(value) { add2(value) } calculate(2)
{-}
Error: Unexpected '}' in {.tabset}
Problem
The cats() function determines cat vocalisations based on their age.
cats <- data.frame(name = c("Cady", "Kitten", "Cleo"), age = c(15, 14, 3)) for (i in 1:3) { cat <- cats[i, ] if (cat$age > 10) { for (j in seq_len(cat$age)) { meows <- rep("Meeooooww!", cat$age) } } msg <- paste(cat$name, "Meeooooww!") } } else { msg <- paste(cat$name, "Pew! Pew!") } print(msg) }
Hints
There are too many brackets here. It's easier to see which opening and closing
brackets match by highlighting the lines (or pressing Command + A on a Mac
/ Ctrl + A on Windows), then using the Reindent Lines shortcut (in the menu
bar, select Code, then Reindent Lines; or pressing Command + I on a Mac /
Ctrl + I on Windows).
There are two extra curly brackets on lines 10 and 12.
To make the code easier to read, even more curly brackets can be removed.
Since both the contents of the for loop and the contents of the else
statement comprise only a single line.
Solution
cats <- data.frame(name = c("Cady", "Kitten", "Cleo"), age = c(15, 14, 3)) for (i in 1:3) { cat <- cats[i, ] if (cat$age > 10) { for (j in seq_len(cat$age)) meows <- rep("Meeooooww!", cat$age) msg <- paste(cat$name, "Meeooooww!") } else msg <- paste(cat$name, "Pew! Pew!") print(msg) }
{-}
Error: unexpected '=' in {.tabset}
Problem
Define a countdown() function, which counts down from a number before
printing "Blast off!" to the console.
countdown <- function(number) { if (number < 0) { stop("Can't countdown from a negative time.") } else { timestep <- number for (i in 1:number) { print(timestep) timestep <- timestep - 1 Sys.sleep(1) if (timestep = 0) print("Blast off!") } } } countdown(3)
Hints
As the error stated, R has found an unexpected =:
Here, the code stops after hitting the first error. That's because of the way
this website is generated. In RStudio, a number of unexpected '}' in ...
errors follow this. The number of errors here might seem intimidating, but the
important thing to note is that after we fix the first one, the remaining three
will cease to occur. It's very important, therefore, to tackle errors in
sequence.
So, returning to the unexpected =... the only = can be found on line 19.
Now, recall that if statements are always followed by a condition. That is,
a conditional test that results in TRUE or FALSE.
Solution
countdown <- function(number) { if (number < 0) { stop("Can't countdown from a negative time.") } else { timestep <- number for (i in 1:number) { print(timestep) timestep <- timestep - 1 Sys.sleep(1) if (timestep == 0) # fix conditional test print("Blast off!") } } } countdown(3)
{-}
Error: object not found {.tabset}
Problem
Given an acceleration from a point of rest and a time of travel, calculate the displacement of an object using Newton's second equation of motion:
$$s = ut + \frac{1}{2}at^2$$
displacement <- function(acceleration, time) { starting_speed <- 0 initial_velocity * time + (0.5 * acceleration * (time ^ 2)) } displacement(10, 18)
Hints
Here, an error is generated on line 3 when R tries to multiply
initial_velocity by time, but can't find an initial_velocity object:
If an object is not defined earlier in the function, then it must be passed as an argument. It can't just magically appear out of thin air!
Solution
displacement <- function(acceleration, time) { initial_velocity <- 0 # initialise the object here! initial_velocity * time + (0.5 * acceleration * (time ^ 2)) } displacement(10, 18)
{-}
Error: missing value where TRUE/FALSE needed {.tabset}
Problem
The checker() function checks whether a number is big (greater than 10) or
small (less than or equal to 10) and prints out a descriptive statement to the
console.
checker <- function(value) { if (value > 10) { print("Big number") } else { print("Small number") } } items <- list(2, 8, NA, 32) for (i in items) { checker(i) }
Hints
Here, R is returning an error on the third iteration of the for loop:
There if an error in if (value > 10) because a TRUE/FALSE value is expected.
In this case, checker() is trying to determine whether the value, NA, is
greater than 10. Since NA > 10 returns NA and if else statements only
accept boolean values, an error is generated.
Solution
The solution here is to either remove NA from the items vector or check for
non-numeric values in the function.
checker <- function(value) { if (!is.numeric(value)) { # check for print("Not a number") # non-numeric } else if (value > 10) { # values here! print("Big number") } else { print("Small number") } } items <- list(2, 8, NA, 32) for (i in items) { checker(i) }
{-}
Warning: the condition has length > 1 and only the first element will be used {.tabset}
Problem
The function explode() takes a number between 0 and 11, otherwise NA is
returned. Values between 0 and 10 are incremented by 1, whereas 11 is reset
to 0.
explode <- function(value) { if (value > 11) { output <- NA } else if (value == 11) { output <- 0 } else { output <- value + 1 } output } vector <- c(2, 4, 11, 27, 15) explode(vector)
Hints
Here we have a warning that has been triggered by if (value > 11). In this
case, it's particularly dangerous because a Warning doesn't stop your code
like an Error does, and here, erroneous values are returned!
The warnings are triggered on lines 3 and 7, where vector (a five element
vector) is passed into explode() as the value argument.
The problem is that the condition (if (condition)) must have a length of 1
and therefore only the first element of the vector is being used in the
comparison. That is, value is input as c(2, 4, 11, 27, 15), but the
condition value > 11 tests on 2, returning FALSE. Then the condition
value == 11 tests on 2, again returning FALSE. So then output <- value + 1
returns c(3, 5, 12, 28, 16).
Solution
The solution here is to either (1) ensure the function can only take a single
input value; or (2) wrap the if else statements in a for loop, so that
each element of the vector can be checked and transformed individually. Here
we do the former:
explode <- function(value) { if (length(value) > 1) # add a check stop("Input must be a single value") # here if (value > 11) { output <- NA } else if (value == 11) { output <- 0 } else { output <- value + 1 } output } vector <- c(2, 4, 11, 27, 15) for (i in vector) { # and loop explode(i) # through the } # vector here
{-}
Error: unexpected symbol in {.tabset}
Problem
The quadratic() function is used to solve quadratic equations.
quadratic <- function(a, b, c) { root <- sqrt(b^2 - 4ac) solution1 <- -b + root / 2a solution2 <- -b - root / 2a list(solution1 solution2) } quadratic(1, -5, 6)
Hints
An unexpected symbol can often be avoided by keeping good code hygiene and
making sure everything is neat and tidy. A good way to do this is to make
good use of white space (blank lines between sections of code) as well as
making a habit of selecting all of your code (Command + A on Mac /
Ctrl + A on Windows), then reindenting your lines (Command + I on Mac /
Ctrl + I on Windows).
In this case, that won't help because each error occurs on a single line. There are 4 syntax errors -- errors in the grammar of code -- in total, see if you can find them all.
Solution
quadratic <- function(a, b, c) { root <- sqrt(b^2 - 4 * a * c) # here, solution1 <- -b + root / 2 * a # here, solution2 <- -b - root / 2 * a # here, list(solution1, solution2) # and here! } quadratic(1, -5, 6)
{-}
Error: replacement has, data has {.tabset}
Problem
There are no functions here. We only wish to add a new column to a dataframe.
data <- data.frame(colour = c("teal", "mustard yellow", "leaf green", "dark", "candyfloss pink", "quite a nice brown"), number = c(3328476, 9832, 23992611, 213987, 487621, 6328974)) data$time <- seq(0, 9, 2)
Hints
This error is a little difficult to read:
The key point to note here is that the replacement has 5 rows but the data
has 6... and the replacement here is time.
Solution
data <- data.frame(colour = c("teal", "mustard yellow", "leaf green", "dark", "candyfloss pink", "quite a nice brown"), number = c(3328476, 9832, 23992611, 213987, 487621, 6328974)) data$time <- seq(0, 9, 1.67)
{-}
Error: object of type 'closure' is not subsettable {.tabset}
Problem
The force() function calculates Newton's second law of motion.
force <- function(mass, acceleration) { mass * acceleration } dat <- data.frame(mass = c(20, 23, 27), acceleration = c(30, 40, 62)) for (i in seq_len(nrow(dat))) { mean[i] <- force(dat$mass[i], dat$acceleration[i]) } mean
Hints
This is a tricky one that might require an internet search (for Stack Overflow) to solve.
Reading the error message, we know that the error is
triggered on line 11 by mean[i] <- force(dat$mass[i], dat$acceleration[i]):
The problem is that "object of type 'closure' is not subsettable". What does this mean?
Solution
force <- function(mass, acceleration) { mass * acceleration } dat <- data.frame(mass = c(20, 23, 27), acceleration = c(30, 40, 62)) results <- c() # define results object first and don't give an object # the same name as a function! for (i in seq_len(nrow(dat))) { results[i] <- force(dat$mass[i], dat$acceleration[i]) } results
{-}
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