Suppose that I have a 90x4 matrix, say matrixgroup1, and some of rows are zero vectors. I want to find the rows that are not zero vectors. The code that I try was:

``which(matrixgroup1[,1:4]!=c(0,0,0,0))``

and it gave the result as

``  1 9 19 28 59 60 62 91 99 109 118 149 150 152 181 189 199 208 239 240 242 271 279 289 298 329 330 332``

However the right columns should be `1 9 19 28 59 60 62` . I don't know where the remaining 91-332 came from.

Since I am new to R, it's quite hard for me to figure it out. Can someone help me and give me the right code ? Thanks in advance.

Simply:

`rowSums(matrixgroup1) != 0`

I dont know, if it can be done better than this, but a solution would be to sum up each column seperately, and then check which of them is different from zero:

``````colcount<- ncol(matrixgroup1)
matrixgroup1NEW<-0
for(i in 1:colcount){
matrixgroup1NEW[i]<-sum(matrixgroup1[,i])
}
which(matrixgroup1NEW!=0)
``````

EDIT: thought you wanted which was zero. Changed to check which is nonzero

Creating a matrix with one "zero" row:

``````myMat <- cbind(x1 = c(1, 3, 8, 0, 1, 3), x2 = c(2, 4, 0, 0, 1, 0))
``````

Getting the non-zero rows in the matrix:

``````myMat[which(!rowSums(myMat) == 0),]
``````

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