What is apply function in R?
This recipe explains what is apply function in R
Recipe Objective
Problem: Iteration through a long list or vector using a for loop takes tremendous amount of time.
This problem is solved by using apply family of functions in R. This family of functions can be fed with many built-in functions to perform different tasks on the collection of objects such as list, vector, dataframe etc.
The family of apply functions are listed below:
- apply()
- lapply()
- sapply()
- tapply()
apply() is a function that takes a matrix or dataframe as input and gives the output in vector or array by appplying a certain operation on it.
This recipe demonstrates how to use the apply() using dataframe as input
Step 1: Importing libraries and loading dataset
Dataset description: It is the basic data about the customers going to the supermarket mall. The variable that we interested in is Annual.Income which is in 1000s and Spending Score
# Data manipulation package
library(tidyverse)
​
# reading a dataset
customer_seg = read.csv('R_72_Mall_Customers.csv')
​
glimpse(customer_seg)
Rows: 200 Columns: 5 $ CustomerID1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 1... $ Gender Male, Male, Female, Female, Female, Female, ... $ Age 19, 21, 20, 23, 31, 22, 35, 23, 64, 30, 67, ... $ Annual.Income..k.. 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 19, ... $ Spending.Score..1.100. 39, 81, 6, 77, 40, 76, 6, 94, 3, 72, 14, 99,...
Step 2: Using apply()
Using the apply() with the following syntax:
apply(X, MARGIN, FUN)
where:
- X = data frame or matrix ;
- MARGIN = an argument which represents the dimension in which the operation should take place (row or column wise). 1 for row-wise and 2 for column wise ;
- FUN = function that needs to be applied on every element of the dataframe
# applying sum function on 2 columns "Annual income" and "spending score"
result = apply(customer_seg[,c("Annual.Income..k..","Spending.Score..1.100.")], MARGIN = 2, FUN = sum)
​
result
Annual.Income..k..12112Spending.Score..1.100.10040
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