Sorry, there may be some lingo for describing the extraction problem I have,
but I don't know it.
I have a matrix of 2 rows and N columns, and a vector of N 1s and 2s.
Matrix M:
1 2 3 4 ... N
1 A C D G ...
2 B D F H ...
Vector v:
1 2 2 1 2 1 1 ... N
I'd like to apply v to M to get
Vector w:
A D F G ...
I.e. each element of v is interpreted as a row-index used to extract that
row's value from the corresponding column in M into the corresponding column
of w.
Also eventually nrow(M) > 2, in which case the value of the elements of v
would range over 1:nrow(M).
Seems it should be simple, but maybe not?
Thanks!
Doug
PS : I originally posted this on "R devel", then realized my mistake. "Move
thread" didn't work when I tried it, though.
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