case_when: A general vectorised if

In YTLogos/dplyr: A Grammar of Data Manipulation

Description

This function allows you to vectorise multiple if and else if statements. It is an R equivalent of the SQL CASE WHEN statement.

Usage

case_when(...)

Arguments

...

A sequence of two-sided formulas. The left hand side (LHS) determines which values match this case. The right hand side (RHS) provides the replacement value. The LHS must evaluate to a logical vector. Each logical vector can either have length 1 or a common length. All RHSs must evaluate to the same type of vector. These dots are evaluated with explicit splicing.

Value

A vector as long as the longest LHS, with the type (and attributes) of the first RHS. Inconsistent lengths or types will generate an error.

Examples

x <- 1:50
case_when(
  x %% 35 == 0 ~ "fizz buzz",
  x %% 5 == 0 ~ "fizz",
  x %% 7 == 0 ~ "buzz",
  TRUE ~ as.character(x)
)

# Like an if statement, the arguments are evaluated in order, so you must
# proceed from the most specific to the most general. This won't work:
case_when(
  TRUE ~ as.character(x),
  x %%  5 == 0 ~ "fizz",
  x %%  7 == 0 ~ "buzz",
  x %% 35 == 0 ~ "fizz buzz"
)

# case_when is particularly useful inside mutate when you want to
# create a new variable that relies on a complex combination of existing
# variables
starwars %>%
  select(name:mass, gender, species) %>%
  mutate(
    type = case_when(
      height > 200 | mass > 200 ~ "large",
      species == "Droid"        ~ "robot",
      TRUE                      ~  "other"
    )
  )

# Dots support splicing:
patterns <- list(
  TRUE ~ as.character(x),
  x %%  5 == 0 ~ "fizz",
  x %%  7 == 0 ~ "buzz",
  x %% 35 == 0 ~ "fizz buzz"
)
case_when(!!! patterns)

YTLogos/dplyr documentation built on May 20, 2019, 1:44 p.m.