R : Apply Function on Rows

This tutorial explains how to apply functions on rows.

Sample Data

data = read.table(text="
XYZ
650
63NA
615
853
1NA 1
872
202", header=TRUE)

Apply Function

When we want to apply a function to the rows or columns of a matrix or data frame. It cannot be applied on lists or vectors.

apply arguments

Calculate maximum value across row

apply(data, 1, max)

It returns NA if NAs exist in a row. To ignore NAs, you can use the following line of code.

apply(data, 1, max, na.rm = TRUE)

Calculate mean value across row

apply(data, 1, mean)
apply(data, 1, mean, na.rm = TRUE)

Calculate number of 0s in each row

apply(data == 0, 1, sum, na.rm= TRUE)

Calculate number of values greater than 5 in each row

apply(data > 5, 1,  sum, na.rm= TRUE)

Select all rows having mean value greater than or equal to 4

df = data[apply(data, 1, mean, na.rm = TRUE)>=4,]

Remove rows having NAs

helper = apply(data, 1, function(x){any(is.na(x))})
df2 = data[!helper,]

It can be easily done with df2 = na.omit(data).

Count unique values across row

df3 = apply(data,1, function(x) length(unique(na.omit(x))))