[R] Fast multiple match function

Keshav Dhandhania kshav.91 at gmail.com
Mon Apr 6 22:56:30 CEST 2015


I know that one can find all occurrences of x in a vector v by doing
> which(x == v).

However, if I need to do this again and again, where v is remaining the
same, then this is quite inefficient. In my particular case, I need to do
this millions of times, and length(v) = 100 million.

Does anyone have suggestion on how to go about it?
I know of a package called fmatch that does the above for the match
function. But they don't handle multiple matches.


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