@cols[1 .. $#cols] = map(tr /[1,2]/[0,1]/, @cols)

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I'm no tr expert, but isn't tr /[1,2]/[0,1]/ more simply written as tr/12/01/?

The following will replace all 1's with 0's, and all 2's with 1's, in all elements of the @cols array. It modifies the array in-place. 

map { tr/12/01/ } @cols;

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Update: I concur with AnonyMonk's hint that it is better written as: 

tr/12/01/ for @cols;

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In reply to Re^3: Hash of Arrays and File Operations by toolic
in thread Hash of Arrays and File Operations by snape

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