[R] How to apply table() on subdata and stack outputs

[Uwe Ligges]

Sean Zhang wrote:
> Dear R helpers:
> 
> I am a R novice and have a question about using table() to extract
> frequences over many sub-datasets.
> A small example input dataframe and wanted output dataframe are provided
> below. The real data is very large so a for loop is what I try to avoid.
> 
> Can someone englithen me how to use sapply or the like to achieve it?


I'd simply use

   table(input.df)

or perhaps closer to the result you want:

  reshape(as.data.frame(table(input.df)), direction="wide",
          timevar="var_interest")


Uwe Ligges



> Many thanks in advance!
> 
> -Sean
> 
> #example input dataframe
> id <- c('tom', 'tom', 'tom', 'jack', 'jack', 'jack', 'jack')
> var_interest <- c("happy","unhappy", "", "happy", "unhappy", 'soso','happy')
> input.df <- data.frame(id=id, var_interest=var_interest)
> input.df
> wanted.df <-
> 
> #output dataframe I want
> id_unique <- c('tom','jack')
> happy_freq<-c(1,2)
> unhappy_freq<-c(1,1)
> soso_freq<-c(0,1)
> miss_freq<-c(1,0)
> output.df <-data.frame(id_unique=id_unique, happy_freq=happy_freq,
> unhappy_freq=unhappy_freq, soso_freq=soso_freq, miss_freq=miss_freq)
> output.df
> 
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> 
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