R store output from lapply with multiple functions

Question

I'm using lapply to loop through a list of dataframes and apply the same set of functions. This works fine when lapply has just one function, but I'm struggling to see how I store/print the output from multiple functions - in that case, I seem to only get output from one 'loop'.

So this:

output <- lapply(dflis,function(lismember) vss(ISEQData,n=9,rotate="oblimin",diagonal=F,fm="ml"))

works, while the following doesn't:

output <- lapply(dflis,function(lismember){
outputvss <- vss(lismember,n=9,rotate="oblimin",diagonal=F,fm="ml")
nefa <- (EFA.Comp.Data(Data=lismember, F.Max=9, Graph=T))
})

I think this dummy example is an analogue, so in other words:

nbs <- list(1==1,2==2,3==3,4==4)
nbsout <- lapply(nbs,function(x) length(x))

Gives me something I can access, while I can't see how to store output using the below (e.g. the attempt to use nbsout[[x]][2]):

nbs <- list(1==1,2==2,3==3,4==4)
nbsout <- lapply(nbs,function(x){
  nbsout[[x]][1]<-typeof(x)
  nbsout[[x]][2]<-length(x)
  }
                 )

I'm using RStudio and will then be printing outputs/knitting html (where it makes sense to display the results from each dataset together, rather than each function-output for each dataset sequentially).

agstudy · Accepted Answer · 2015-01-11 13:39:44Z

3

You should return a structure that include all your outputs. Better to return a named list. You can also return a data.frame if your outputs have all the same dimensions.

otutput <- lapply(dflis,function(lismember){
    outputvss <- vss(lismember,n=9,rotate="oblimin",diagonal=F,fm="ml")
    nefa <- (EFA.Comp.Data(Data=lismember, F.Max=9, Graph=T))

    list(outputvss=outputvss,nefa=nefa)  
    ## or data.frame(outputvss=outputvss,nefa=nefa) 
})

When you return a data.frame you can use sapply that simply outputs the final result to a big data.frame. Or you can use the classical:

do.call(rbind,output)

to aggregate the result.

edited Jan 11, 2015 at 13:39

answered Jan 11, 2015 at 13:31

agstudy

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Roland · Accepted Answer · 2015-01-11 13:29:48Z

2

A function should always have an explicit return value, e.g.

output <- lapply(dflis,function(lismember){
   outputvss <- vss(lismember,n=9,rotate="oblimin",diagonal=F,fm="ml")
   nefa <- (EFA.Comp.Data(Data=lismember, F.Max=9, Graph=T))
   #return value:
   list(outputvss, nefa)
})

output is then a list of lists.

answered Jan 11, 2015 at 13:29

Roland

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6 Comments

David Arenburg Over a year ago

I guess it will be easier to access the values if they would use c instead of list (at least for their reproducible example, when the result is just one value per function)

agstudy Over a year ago

@DavidArenburg c is just a shortcut for a list, isn't?

David Arenburg Over a year ago

@agstudy, the output is a vector per each argument within the list, instead of list per each argument within the list. Try lapply(nbs, function(x){ nbsout1<-typeof(x) ; nbsout2<-length(x); c(nbsout1, nbsout2)})

agstudy Over a year ago

@DavidArenburg but you assume that the 2 has the same dimensions , indeed c will unlist the result to get the same vector ....

Roland Over a year ago

@DavidArenburg Maybe. This is just an example. I have no idea what kind of objects outputvss and nefa are.

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