What are the different types of iterations in R?
Marvah MushtaqOverview
In R, iteration is not preferred because it’s computationally expensive.
Apart from the basic looping functions like for and while, R also supports the following vectorized looping functions:
apply()lapply()tapply()sapply()by()
The primary goal of these functions is to avoid using loop structures explicitly. They can apply a function on an input list, matrix, or array. These functions accept any function as a parameter.
We’ll be looking into three main functions in detail in this shot.
The apply() function
The apply() function accepts a data frame, vector, list, or array as input and returns a data frame, vector, list, or array as output.
Syntax
apply(X, MARGIN, FUN)
Arguments
X: This is a data frame, vector, list, or array.MARGIN: This takes a value or range between1and2to define where to apply the function, e.g.:MARGIN=1: The manipulation is performed on rows.MARGIN=2: The manipulation is performed on columns.MARGIN=c(1,2)The manipulation is performed on rows and columns.
FUN: This specifies which function should be used. Mean, median, sum, min, max, and other built-in functions, as well as user-defined functions, can be used.
Code
Let’s look at the following example.
df <- data.frame(x = 1:4, y = 5:8, z = 10:13) #df x y z # 1 5 10 = 16 (sum by row) # 2 6 11 = 19 (sum by row) # 3 7 12 = 22 (sum by row) # 4 8 13 = 25 (sum by row) # Sum by row apply(X = df, MARGIN = 1, FUN = sum)
Explanation
- Line 1: This defines the data frame named
df. - Line 10: This outputs the summed by row values as shown in lines 3-7.
The lapply() function
The lapply() function can be used to perform operations on a list or vector that returns a list or vector of the same length as the original with the resultant elements obtained after applying the specified FUN.
Syntax
lapply(X, FUN)
Arguments
X: This is a list or vector.FUN: This is the function to be applied on each element ofX.
Code
Let’s look at the following example.
movies <- c("SPYDERMAN","BATMAN","VERTIGO","CHINATOWN")
movies_lower <- lapply(movies, tolower)
str(movies_lower)Explanation
- Line 1: This defines the vector named
movies. - Line 2: This applies the
tolowerfunction and stores the results tomovies_lower. - Line 3: This displays the structure of
movies_lower.
The sapply() function
The sapply() function accepts a vector, list, or array as input and returns a vector, list, or array as output.
Syntax
sapply(X, FUN)
Arguments
X: This is a vector, list, or array.FUN: This is a function applied to each element ofX.
Code
Let’s look at the following example.
data <- list(item1 = 1:5,
item2 = seq(4,36,8),
item4 = c(1,3,5,7,9))
# $item1
# [1] 1 2 3 4 5 = 15 (summed)
# $item2
# [1] 4 12 20 28 36 = 100 (summed)
# $item4
# [1] 1 3 5 7 9 = 25 (summed)
sapply(data, sum)Explanation
- Lines 1-3: This defines the list named
data. - Line 12: This sums and displays the values of
dataas shown in lines 5-10.
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Marvah MushtaqView all Courses
