which() Function in R (original) (raw)

Last Updated : 23 Aug, 2021

which() function in R Programming Language is used to return the position of the specified values in the logical vector.

Syntax: which(x, arr.ind, useNames)

Parameters: This function accepts some parameters which are illustrated below:

• X: This is the specified input logical vector
• Arr.ind: This parameterreturns the array indices if x is an array.
• useNames: This parameter says the dimension names of an array.

Return value: This function returns the position of the specified values in the logical vector.

Example 1: Which() function applying tothe alphabet

In the below example, which() function returns the alphabetical position of the specified letter. For example, a is the first letter in the alphabet sequence that's why 1 is returned and z is the last letter in the sequence so 26 is returned.

R `

R program to illustrate

which() function

Calling the which function

to return alphabetical position

of the given alphabet

which(letters == "a") which(letters == "d") which(letters == "z") which(letters == "p") which(letters == "g")

`

Output :

[1] 1 [1] 4 [1] 26 [1] 16 [1] 7

Example 2: which() function with vectors

In the below example, the position of some elements of the specified vector is being returned which the help of which() function.

R `

R program to illustrate

which() function

Creating a vector of some elements

vector <- c(3, 5, 1, 6, 12, 4)

Getting the position of element 12

in the above vector

which(vector == 12)

Getting the position of element 1

in the above vector

which(vector == 1)

Getting the position of element 6

in the above vector

which(vector == 6)

Getting the position of elements

those are greater than 5

which(vector > 5)

`

Output:

[1] 5 [1] 3 [1] 4 [1] 4 5

Example 3: which() function with dataframe

In the below example, which() function is used to find the columns in a data frame with numeric values.

An Iris data set is used as a data frame that contains 4 columns for numerical values and 1 column for categorical values i.e., Species. The which() function find the columns name from the data set that contain numeric values.

R `

Considering “Iris” dataset

data_set <- datasets::iris

Printing the Iris dataset values

along with its 5 columns out of which

4 columns are numerical and 1 is categorical

(Species)

head(data_set)

Calling the which() function over

the above specified data set that

returns the columns with numeric values

Result <- which(sapply(data_set, is.numeric))

Printing the columns with numeric values

colnames(data_set)[Result]

`

Output:

Example 4: which() function with the matrix

In the below example, which() function is used to find the position of an element in the specified matrix.

Here the position of value 2 in the specified matrix is being calculated.

R `

Creating a matrix of 3 columns and 4 rows

Matrix <- matrix(rep(c(1, 2, 3), 4), nrow = 4)

Printing the entire matrix with its values

Matrix

Calling the which() function to find the

position of value 2 in the above matrix

which(Matrix == 2, arr.ind = T)

`

Output: