vlookup: Look up values in dictionary.

In maditr: Fast Data Aggregation, Modification, and Filtering with Pipes and 'data.table'

Look up values in dictionary.

Description

vlookup function is inspired by VLOOKUP spreadsheet function. It looks for a lookup_value in the lookup_column of the dict, and then returns values in the same rows from result_column. xlookup is simplified version of vlookup. It searches for a lookup_value in the lookup_vector and return values in the same position from the result_vector.

Usage

vlookup(
  lookup_value,
  dict,
  result_column = 2,
  lookup_column = 1,
  no_match = NA
)

xlookup(lookup_value, lookup_vector, result_vector, no_match = NA)

Arguments

lookup_value	Vector of looked up values
dict	data.frame. Dictionary.
result_column	numeric or character. Resulting columns in the dict. Default value for result_column is 2 - for frequent case of dictionary with keys in the first column and results in the second column.
lookup_column	Column of dict in which lookup value will be searched. By default, it is the first column of the dict.
no_match	vector of length one. NA by default. Where a valid match is not found, return the 'no_match' value you supply.
lookup_vector	vector in which 'lookup_value' will be searched during 'xlookup'.
result_vector	vector with resulting values for 'xlookup'.

Value

xlookup always return vector, vlookup returns vector if the result_column is single value. In the opposite case data.frame will be returned.

Examples

# with data.frame
dict = data.frame(num=1:26, small=letters, cap=LETTERS)
vlookup(1:3, dict)
vlookup(c(45,1:3,58), dict, result_column='cap')
vlookup(c(45,1:3,58), dict, result_column='cap', no_match = "Not found")

# the same with xlookup
xlookup(1:3, dict$num, dict$small)
xlookup(c(45,1:3,58), dict$num, dict$cap)
xlookup(c(45,1:3,58), dict$num, dict$cap, no_match = "Not found")


# example from base 'merge'
authors = data.table(
    surname = c("Tukey", "Venables", "Tierney", "Ripley", "McNeil"),
    nationality = c("US", "Australia", "US", "UK", "Australia"),
    deceased = c("yes", rep("no", 4))
)

books = data.table(
    surname = c("Tukey", "Venables", "Tierney",
                "Ripley", "Ripley", "McNeil", "R Core"),
    title = c("Exploratory Data Analysis",
              "Modern Applied Statistics ...",
              "LISP-STAT",
              "Spatial Statistics", "Stochastic Simulation",
              "Interactive Data Analysis",
              "An Introduction to R")
)

let(books,
     c("author_nationality", "author_deceased") := vlookup(surname,
             dict = authors,
             result_column = 2:3
         )
)[]

# Just for fun. Examples borrowed from Microsoft Excel.
# It is not the R way of doing things.

# Example 2

ex2 = fread("
    Item_ID Item Cost Markup
    ST-340 Stroller 145.67  0.30
    BI-567 Bib 3.56  0.40
    DI-328 Diapers  21.45  0.35
    WI-989 Wipes  5.12  0.40
    AS-469 Aspirator 2.56  0.45
")

# Calculates the retail price of diapers by adding the markup percentage to the cost.
vlookup("DI-328", ex2, 3) * (1 + vlookup("DI-328", ex2, 4)) # 28.9575

# Calculates the sale price of wipes by subtracting a specified discount from
# the retail price.
(vlookup("WI-989", ex2, "Cost") * (1 + vlookup("WI-989", ex2, "Markup"))) * (1 - 0.2)  # 5.7344

A2 = ex2[["Item_ID"]][1]
A3 = ex2[["Item_ID"]][2]

# If the cost of an item is greater than or equal to $20.00, displays the string
# "Markup is nn%"; otherwise, displays the string "Cost is under $20.00".
ifelse(vlookup(A2, ex2, "Cost") >= 20,
       paste0("Markup is " , 100 * vlookup(A2, ex2, "Markup"),"%"),
       "Cost is under $20.00") # Markup is 30%


# If the cost of an item is greater than or equal to $20.00, displays the string
# Markup is nn%"; otherwise, displays the string "Cost is $n.nn".
ifelse(vlookup(A3, ex2, "Cost") >= 20,
       paste0("Markup is: " , 100 * vlookup(A3, ex2, "Markup") , "%"),
       paste0("Cost is $", vlookup(A3, ex2, "Cost"))) #Cost is $3.56


# Example 3

ex3 = fread('
    ID  Last_name  First_name  Title Birth_date
    1 Davis Sara "Sales Rep."  12/8/1968
    2 Fontana Olivier "V.P. of Sales" 2/19/1952
    3 Leal Karina "Sales Rep." 8/30/1963
    4 Patten Michael "Sales Rep." 9/19/1958
    5 Burke Brian "Sales Mgr." 3/4/1955
    6 Sousa Luis "Sales Rep."  7/2/1963
')

# If there is an employee with an ID of 5, displays the employee's last name;
# otherwise, displays the message "Employee not found".
vlookup(5, ex3, "Last_name", no_match = "Employee not found") # Burke

# Many employees
vlookup(1:10, ex3, "Last_name", no_match =  "Employee not found")

# For the employee with an ID of 4, concatenates the values of three cells into
# a complete sentence.
paste0(vlookup(4, ex3, "First_name"), " ",
       vlookup(4, ex3, "Last_name"), " is a ",
       vlookup(4, ex3, "Title")) # Michael Patten is a Sales Rep.

maditr documentation built on April 2, 2022, 5:05 p.m.