Hi Kate,

You could try

sum(X[, 1] == 1 &  X[, 2] == 1)

where X is your data set.

HTH,
Jorge.-



On Sun, Jun 22, 2014 at 12:57 AM, Kate Ignatius <kate.ignatius@gmail.com>
wrote:

> I have 4 columns, and about 300K plus rows with 0s and 1s.
>
> I'm trying to count how many rows satisfy a certain criteria... for
> instance, how many rows are there that have the first column == 1 as
> well as the second column == 1.
>
> I've tried using rowSums and colSums but it keeps giving me this type of
> error:
>
> Error in rowSums(X[1] == 1 & X[2] == 1) :
>   'x' must be an array of at least two dimensions
>
> Thanks in advance!
>
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