[R] Warning: matrix by vector division

From: Alexey Shipunov <dactylorhiza_at_gmail.com>
Date: Fri, 07 Mar 2008 17:32:44 -0500


Dear list,

I just made a very simple mistake, but it was hard to spot. And I think that I should warn other people, because it is probably so simple to make...

# Let us create a matrix:

(a <- cbind(c(0,1,1), rep(1,3)))

# [,1] [,2]
# [1,] 0 1
# [2,] 1 1
# [3,] 1 1

# That is a MISTAKE:

a/colSums(a)

# [,1] [,2]
# [1,] 0.0000000 0.3333333
# [2,] 0.3333333 0.5000000
# [3,] 0.5000000 0.3333333
# I just wonder if some R warning should be issued here?

# That is what I actually needed (column-wise frequencies):
t(t(a)/colSums(a))

# [,1] [,2]
# [1,] 0.0 0.3333333
# [2,] 0.5 0.3333333
# [3,] 0.5 0.3333333

With best wishes and regards,
Alexey Shipunov



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