How to select only numeric columns from an R data frame?

The easiest way to do it is by using select_if function of dplyr package but we can also do it through lapply.

Using dplyr

> df <- data.frame(X1=1:10,X2=11:20,X3=21:30,X4=letters[1:10], X5=letters[11:20])
> df
X1 X2 X3 X4 X5
1 1 11 21 a k
2 2 12 22 b l
3 3 13 23 c m
4 4 14 24 d n
5 5 15 25 e o
6 6 16 26 f p
7 7 17 27 g q
8 8 18 28 h r
9 9 19 29 i s
10 10 20 30 j t
>library("dplyr")
> select_if(df, is.numeric)
X1 X2 X3
1 1 11 21
2 2 12 22
3 3 13 23
4 4 14 24
5 5 15 25
6 6 16 26
7 7 17 27
8 8 18 28
9 9 19 29
10 10 20 30

Using lapply

> numeric_only <- unlist(lapply(df, is.numeric))
> df[ , numeric_only]
  X1 X2 X3
1 1 11 21
2 2 12 22
3 3 13 23
4 4 14 24
5 5 15 25
6 6 16 26
7 7 17 27
8 8 18 28
9 9 19 29
10 10 20 30