[R] Sum of Probabilities in a matrix...

[Dennis Murphy]

Let's make it a data frame instead:

# Read the data from your post into a data frame named d:
d <- read.table(textConnection("
0.98   2
0.2     1
0.01   2
0.5     1
0.6     6"))
closeAllConnections()

# Use the ave() function and append the result to d:
d$sumprob <- with(d, ave(V1, V2, FUN = sum))

> d
    V1 V2 sumprob
1 0.98  2    0.99
2 0.20  1    0.70
3 0.01  2    0.99
4 0.50  1    0.70
5 0.60  6    0.60

HTH,
Dennis

On Sat, Oct 1, 2011 at 6:06 PM, Jim Silverton <jim.silverton at gmail.com> wrote:
> Hi all,
> I have 2 columns in a mtrix, one of which is a column of probabilities and
> the other is simply a vector of integers. I want to sum all the
> probabilities with the same integer value and put it in a new column.
> For example,
> If my matrix is:
>
> 0.98   2
> 0.2     1
> 0.01   2
> 0.5     1
> 0.6     6
>
>
> Then I should get:
> 0.98   2    0.99
> 0.2     1    0.70
> 0.01   2    0.99
> 0.5     1    0.70
> 0.6     6    0.60
>
> Any help is greatly appreciated.
>
>
>
> --
> Thanks,
> Jim.
>
>        [[alternative HTML version deleted]]
>
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