[R] apply on rows and columns?

[R. Michael Weylandt]

It's the same as what you began with --  and that's because you broke
it down by columns and rows and took the sum of everything that
resulted.

I.e.,

sum(m[1,1])
sum(m[2,1])
sum(m[1,2])
sum(m[2,2])

and put them back together.

Michael

On Wed, Nov 16, 2011 at 3:13 PM,  <rkevinburton at charter.net> wrote:
>
> I have the following scenario:
>
>> m <- matrix(1:4, ncol=2)
>> m
>      [,1] [,2]
> [1,]    1    3
> [2,]    2    4
>> apply(m, 2, sum)
> [1] 3 7
>> apply(m, 1, sum)
> [1] 4 6
>
> So I can apply to rows *or* columns. According to the documentation
> (?apply)
>
> MARGIN a vector giving the subscripts which the function will be applied
> over. E.g., for a matrix 1 indicates rows, 2 indicates columns, c(1, 2)
> indicates rows and columns. Where X has named dimnames, it can be a
> character vector selecting dimension names.
>
>
> But I get the following results:
>
>> apply(m, c(1,2), sum)
>      [,1] [,2]
> [1,]    1    3
> [2,]    2    4
>
> How am I to interpret this result?
>
> Thank you.
>
> Kevin
>
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>
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