[R] lapply, sapply

baptiste auguie ba208 at exeter.ac.uk
Sat Aug 2 12:33:38 CEST 2008

It seems to me that the reshape package should do the job,

library(reshape) # note that you need to fix the method to melt lists  
in the current version ( passing ... to the method for data.frames, as  
discussed here last week)

cast(data=melt(dat), fun.aggregate = function(.x) rle(.x)$length[1])

this works for me, but I have to confess a very limited understanding  
of reshape.

Hope this helps,


On 2 Aug 2008, at 10:07, stefan.duke at gmail.com wrote:

> Hello everybody,
> I have problem with a lapply command, which rather proves that I don't
> fully understand it.
> I want to extract from a list that consists of dataframes, the length
> of the first sequences from a given variable (its part of a simulation
> exercises).
> Below is code which does the job, but I think it should be possible to
> make it more compact.
> ### Example Data
> dat <-list()
> dat[[1]] <- data.frame(matrix( rbinom(40, 1, .8),nrow=5))
> dat[[2]] <- data.frame(matrix( rbinom(40, 1, .8),nrow=5))
> ####Code
> x<-sapply(dat,"[",3)    #Extracting the vector
> y<-lapply(x,rle)          #Counting the sequences which is returned  
> as a list
> z<-sapply(y,"[", 1)     #extracting the first element of the list of
> sequence counts
> final<-sapply(z,"[",1)   #extracting the first number, which gives the
> length of the first sequence, which I want
> final
> ###############
> Thanks for your help,
> Stefan
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Baptiste Auguié

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,

Phone: +44 1392 264187


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