which() Function in R
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 parameter returns 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 to the 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:
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