[R] How do I tapply to a data frame with arbitrary column labels?

[Gabor Grothendieck]

Look at rowsum or aggregate:

> Lines <- "class    pigeon    falcon    propeller    jet    wing    fly
+ birds    25           37          0                0      2        1
+ planes 0             1            28              40    1        3
+ birds    19           41          0                1      4        6
+ planes  0            0            25              50    5        5
+ planes  1            0           30               45    3        5"
>
> DF <- read.table(textConnection(Lines), header = TRUE)

> rowsum(DF[-1], DF[,1])
       pigeon falcon propeller jet wing fly
birds      44     78         0   1    6   7
planes      1      1        83 135    9  13

> aggregate(DF[-1], DF[1], sum)
   class pigeon falcon propeller jet wing fly
1  birds     44     78         0   1    6   7
2 planes      1      1        83 135    9  13


On Thu, Dec 11, 2008 at 6:25 PM, Bill McNeill (UW)
<billmcn at u.washington.edu> wrote:
> I have a data file that looks like this
>
> class    pigeon    falcon    propeller    jet    wing    fly
> birds    25           37          0                0      2        1
> planes 0             1            28              40    1        3
> birds    19           41          0                1      4        6
> planes  0            0            25              50    5        5
> planes  1            0           30               45    3        5
>
> There may be an arbitrary number of unique class labels and an
> arbitrary number of uniquely named columns.  I use read.table to read
> my file into a data frame.  I then want to take the sum of all the
> column values for each of the class types.  That is I want to end up
> with:
>
> class   pigeon    falcon    propeller    jet    wing    fly
> birds    44          78          0                1      6         7
> planes 1             1            83              135  9         13
>
> where (pigeon, birds) = 25 + 19 = 44, (propeller, planes) = 28 + 25 +
> 30 = 83, etc.
>
> I see how to use tapply to get the sum for each individual column, e.g.
>
>> tapply(data$falcon, data$class, sum)
>  birds planes
>    78      1
>
> But I can't figure out what command will do these sums for the entire
> data frame without me having to specify the column names in the
> command.
>
> Thanks.
> --
> Bill McNeill
> http://staff.washington.edu/billmcn/index.shtml
>
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