How to create a table of sums of a discrete variable for two categorical variables in an R data frame?

If we want to create a table of sums of a discrete variable for two categorical variables then xtabs function can be used. The output will be a contingency table or cross tabulation table which looks like a matrix. For example, if we have a data frame df with two categorical column x and y and a count column freq then the table of sums for freq can be created by using xtabs(freq~x+y,data=df1).

Example

Consider the below data frame −

 Live Demo

x1<-sample(c("A","B"),20,replace=TRUE) x2<-sample(c("I","II"),20,replace=TRUE) y1<-rpois(20,5) df1<-data.frame(x1,x2,y1) df1

Output

  x1 x2 y1 1  A II 10 2  A I   5 3  B II  7 4  B I   5 5  B I   7 6  A II  1 7  B II  2 8  B II  3 9  B I   8 10 A I   5 11 A II  8 12 A II  4 13 B I   7 14 B II  4 15 B II  3 16 A I   6 17 A I   4 18 A I   5 19 A II  8 20 A II  7

The creation of cross-tabulation −

Example

xtabs(y1~x1+x2,data=df1) x2

Output

x1 I II A 25 38 B 27 19

Example

 Live Demo

z1<-sample(c("G1","G2","G3","G4"),20,replace=TRUE) z2<-sample(c("S1","S2","S3"),20,replace=TRUE) y2<-sample(1:10,20,replace=TRUE) df2<-data.frame(z1,z2,y2) df2

Output

  z1 z2 y2 1  G2 S1 3 2  G2 S2 9 3  G2 S1 7 4  G2 S3 7 5  G4 S2 3 6  G3 S2 7 7  G2 S2 10 8  G3 S3 1 9  G1 S1 3 10 G4 S1 10 11 G3 S2 4 12 G3 S2 9 13 G2 S1 6 14 G1 S3 3 15 G2 S3 9 16 G1 S3 4 17 G1 S1 9 18 G3 S1 4 19 G4 S2 9 20 G1 S1 6

The creation of cross-tabulation −

Example

xtabs(y2~z1+z2,data=df2) z2

Output

z1 S1 S2 S3 G1 18 0  7 G2 16 19 16 G3 4 20  1 G4 10 12 0