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I have a matrix that I need to filter by a condition.

yj = y[which(g[,j] == 1),]

A problem arises when "which(g[,j] == 1)" is a 1 (or none) component vector. The output, the aforementioned "yj", is then suddenly a vector. I need to be able to reference it by column. Even if it's a single row, it still needs to be reference-able by column.

How do I make this happen?

Faydey
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1 Answers1

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Use drop = FALSE while subsetting. 

yj = y[which(g[,j] == 1),, drop = FALSE]

If which(g[,j] == 1) can be of length 0 better to check for it using if condition. 

inds <- which(g[,j] == 1)
if(inds) yj = y[inds, ,drop = FALSE]
Ronak Shah
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