[R] Extracting data from matrices

[Daniel Bebber]

Dear R list

I have an m * n matrix P and a vector V of length n containing indices for
rows in P.
For each of the m columns I want to extract the value in the row specified
by V, and put these values into a new vector W of length n.
At present I am doing this with a for.... loop, but I imagine there is a faster
way that doesn’t involve loops.
If anyone knows the way I would be most grateful.

Below is the code I am using at present-

for (i in 1:n){
W[i]<-P[V[i],i]}

Many thanks,
Dan Bebber
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