[R] dplyr/summarize does not create a true data frame

[John Kane]

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.posner at mjbiostat.com
> Sent: Fri, 21 Nov 2014 17:10:16 +0000
> To: r-help at 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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