I have a dataframe like this
M2 <- matrix(c(1,0,0,1,1,0,0,1,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0),nrow=7,
dimnames=list(LETTERS[1:7],NULL))
I would like to select the rows based on multiple columns. For instance when I want to select rows based on only two columns, I did
ans<-M2[which(M2[,1]==0 & M2[,2]==0)
But when I want to select only those rows which have value zero based on three or four columns, say based 1, 3, and 4 th column or say 1, 2,3, 4 , how do I do this?
Just for fun a solution that works for a data.frame and could be used for a large number of columns:
DF <- as.data.frame(M2)
DF[rowSums(sapply(DF[,c(1,2,4)],`!=`,e2=0))==0,]
# V1 V2 V3 V4
#B 0 0 0 0
#F 0 0 0 0
#G 0 0 0 0
What happens here?
sapply loops over the columns of the subset DF[,c(1,2,4)]. It applies the function != (not equal) to each column of the subset and compares with 0 (e2 is the second argument of the != function). The result is a matrix of logical values (TRUE/FALSE).rowSums takes the sum of each row of this logical matrix. Logical values are automatically coerced to 1/0. Of course this is easier and faster with a matrix:
M2[rowSums(M2[,c(1,2,4)] != 0) == 0,]
You could use rowSums:
M2[rowSums(M2[,c(1,2,3,4)]) == 0,]
gives you all rows where column 1,2,3 and 4 have a zero:
[,1] [,2] [,3] [,4]
B 0 0 0 0
F 0 0 0 0
G 0 0 0 0
Please note that this won't work if you have positive and negative numbers in you matrix.
M2[rowSums(M2[,c(1,2,3,4)] != 0) == 0,].Your question is not quite clear to me, but is this what you are looking for?
To select based on the values of columns 1 to 4, you will do the following:
ans <- M2[M2[,1]==0 & M2[,2]==0 & M2[,3]==0 & M2[,4]==0,]
#> ans
# [,1] [,2] [,3] [,4]
#B 0 0 0 0
#F 0 0 0 0
#G 0 0 0 0
This will result in the subset of M2 for which all columns 1 to 4 are zero.
whichhere. Isans<-M2[M2[,1]==0 & M2[,2]==0 & M2[,4]==0,]sufficient for your needs?