[R] counting row repetitions without loop
James Foadi
james.foadi at diamond.ac.uk
Wed Feb 6 15:53:12 CET 2008
On Wednesday 06 February 2008 14:08, Waterman, DG (David) wrote:
> Hi,
>
> I have a data frame consisting of coordinates on a 10*10 grid, i.e.
>
> > example
>
> x y
> 1 4 5
> 2 6 7
> 3 6 6
> 4 7 5
> 5 5 7
> 6 6 7
> 7 4 5
> 8 6 7
> 9 7 6
> 10 5 6
>
> What I would like to do is return an 10*10 matrix consisting of counts
> at each position, so in the above example I would have a matrix where,
> for example, cell [4,5] contains 2 and [6,7] contains 3. At the moment I
> have implemented this using a for loop over the rows of the data frame,
> however the data frames I want to process are very long so the loop
> takes many minutes to complete. Can I do this in a more efficient way?
>
> Cheers,
David,
have a look at "mapply" (?mapply). This does what you need very quickly.
J
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