How to subset an R data frame based on small letters?

If we have a data frame that contains some lower case and some upper-case string values then we might want to subset the data frame based on lower case or upper-case letters.

For this purpose, we can make use of apply and sapply function as shown in the below examples.

Example 1

Following snippet creates a sample data frame −

x1<-sample(c(letters[1:26],LETTERS[1:26]),20) x2<-sample(c(letters[1:26],LETTERS[1:26]),20) df1<-data.frame(x1,x2) df1

The following dataframe is created −

  x1 x2 1  w g 2  b l 3  J Z 4  c y 5  Q M 6  T J 7  Z i 8  s c 9  r j 10 E f 11 S N 12 x R 13 n Q 14 v V 15 N n 16 X P 17 p h 18 z I 19 l x 20 P O

To subset df1 based on small letters, add the following code to the above snippet −

x1<-sample(c(letters[1:26],LETTERS[1:26]),20) x2<-sample(c(letters[1:26],LETTERS[1:26]),20) df1<-data.frame(x1,x2) df1[apply(df1==sapply(df1,tolower),1,any),]

Output

If you execute all the above given snippets as a single program, it generates the following output −

   x1 x2 1  w  g 2  b  l 4  c  y 7  Z  i 8  s  c 9  r  j 10 E  f 12 x  R 13 n  Q 14 v  V 15 N  n 17 p  h 18 z  I 19 l  x

Example 2

Following snippet creates a sample data frame −

y1<-sample(c(letters[1:4],LETTERS[1:4]),20,replace=TRUE) y2<-sample(c(letters[1:4],LETTERS[1:4]),20,replace=TRUE) df2<-data.frame(y1,y2) df2

The following dataframe is created −

   y1 y2 1  d  a 2  d  D 3  d  b 4  d  D 5  a  a 6  A  a 7  A  b 8  A  B 9  b  A 10 C  d 11 c  B 12 D  B 13 A  C 14 b  d 15 A  B 16 c  c 17 C  D 18 a  D 19 c  a 20 d  d

To subset df2 based on small letters, add the following code to the above snippet −

y1<-sample(c(letters[1:4],LETTERS[1:4]),20,replace=TRUE) y2<-sample(c(letters[1:4],LETTERS[1:4]),20,replace=TRUE) df2<-data.frame(y1,y2) df2[apply(df2==sapply(df2,tolower),1,any),]

Output

If you execute all the above given snippets as a single program, it generates the following output −

   y1 y2 1  d  a 2  d  D 3  d  b 4  d  D 5  a  a 6  A  a 7  A  b 9  b  A 10 C  d 11 c  B 14 b  d 16 c  c 18 a  D 19 c  a 20 d  d