Your code in creating 'frm' is not working for me and it is complicated enough
that I don't want to work it out. See ?dput for a better way to supply data.
Also see:
https://github.com/hadley/devtools/wiki/Reproducibility
http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example
That said, I don't see why 'my.output[4]' is not working. Try something like
str(frm) to see what you have there and/or resubmit the data in dput format
See simple example below:
dat1 <- data.frame(aa = sample(1:20, 100, replace = TRUE), bb = 1:100 )
dat1[2]
John Kane
Kingston ON Canada
> -----Original Message-----
> From: john.pos...@mjbiostat.com
> Sent: Fri, 21 Nov 2014 17:10:16 +0000
> To: r-help@r-project.org
> Subject: [R] dplyr/summarize does not create a true data frame
>
> I got an error when trying to extract a 1-column subset of a data frame
> (called "my.output") created by dplyr/summarize. The ncol() function says
> that my.output has 4 columns, but "my.output[4]" fails. Note that
> converting my.output using as.data.frame() makes for a happy ending.
>
> Is this the intended behavior of dplyr?
>
> Tx,
> John
>
>> library(dplyr)
>
>> # set up data frame
>> rows = 100
>> repcnt = 50
>> sexes = c("Female", "Male")
>> heights = c("Med", "Short", "Tall")
>
>> frm = data.frame(
> + Id = paste("P", sprintf("%04d", 1:rows), sep=""),
> + Sex = sample(rep(sexes, repcnt), rows, replace=T),
> + Height = sample(rep(heights, repcnt), rows, replace=T),
> + V1 = round(runif(rows)*25, 2) + 50,
> + V2 = round(runif(rows)*1000, 2) + 50,
> + V3 = round(runif(rows)*350, 2) - 175
> + )
>>
>> # use dplyr/summarize to create data frame
>> my.output = frm %>%
> + group_by(Sex, Height) %>%
> + summarize(V1sum=sum(V1), V2sum=sum(V2))
>
>> # work with columns in the output data frame
>> ncol(my.output)
> [1] 4
>
>> my.output[1]
> Source: local data frame [6 x 1]
> Groups: Sex
>
> Sex
> 1 Female
> 2 Female
> 3 Female
> 4 Male
> 5 Male
> 6 Male
>
>> my.output[4]
> Error in eval(expr, envir, enclos) : index out of bounds ######## ERROR
> HERE
>
>> as.data.frame(my.output)[4]
> V2sum
> 1 12427.97
> 2 8449.82
> 3 8610.97
> 4 7249.20
> 5 12616.91
> 6 10372.15
>>
>
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