[R] mapply to lapply

[Kenn Konstabel]

On Mon, Apr 18, 2011 at 2:10 PM, Alaios <alaios at yahoo.com> wrote:
> Dear Andreas,
> I would like to thank you for your reply.
> I have tried two alternatives but none of the two worked out:
>
> F2[i+1,j+1]<-sum(lapply(1:nrow(cells), function(rowInd) Fwithcellvalue(i=i,j=j,a=cells[rowInd,2],b=cells[rowInd,4],c=cells[rowInd,1],d=cells[rowInd,3],e=cells[rowInd,5])))
>
> this one is executed : takes like 2 mins to return(which is normal) but returns the following
>
> ^@Error in sum(lapply(1:nrow(cells), function(rowInd) Fwithcellvalue(i = i,  :
>  invalid 'type' (list) of argument

The lapply part worked but for sum you need a vector rather than a
list (which is the result of lapply). So e.g. sum(unlist(lapply(.....
something .....))) should work.

KK

>
>
> afterwards I tried to change the function definition so to pass i,j inside:
>
> This one does not execute at all
>
> F2[i+1,j+1]<-sum(lapply(1:nrow(cells), function(rowInd,i,j) Fwithcellvalue(i=i,j=j,a=cells[rowInd,2],b=cells[rowInd,4],c=cells[rowInd,1],d=cells[rowInd,3],e=cells[rowInd,5])))
> Error in paste("f", i, j, "(a,b,c,d)", sep = "") :
>  argument "i" is missing, with no default
>
>
> What do you think I should try out now?
>
> Vielen Dank
> Alex
>
> --- On Mon, 4/18/11, Andreas Borg <andreas.borg at unimedizin-mainz.de> wrote:
>
>> From: Andreas Borg <andreas.borg at unimedizin-mainz.de>
>> Subject: Re: [R] mapply to lapply
>> To: "Alaios" <alaios at yahoo.com>
>> Cc: R-help at r-project.org
>> Date: Monday, April 18, 2011, 11:10 AM
>> My solution would be to use an index
>> variable that goes from 1 to the number of rows that are to
>> be processed, along with a helper function which calls
>> Fwithcellvalue with the suitable arguments:
>>
>> F2[i+1,j+1]<-sum(lapply(1:nrow(cells), function(rowInd)
>> Fwithcellvalue(i=i,j=j,a=cells[rowInd,2],b=cells[rowInd,4],c=cells[rowInd,1],d=cells[rowInd,3],e=cells[rowInd,5]))
>>
>>
>> Best regards,
>>
>> Andreas
>>
>> Alaios schrieb:
>> > Dear all,
>> >
>> > I would like to ask your help concerning converting a
>> mapply function to lapply. The reason is that I would like
>> to use mclapply which requires lapply syntax.
>> >
>> > The command I would like to convert is:
>> >
>> F2[i+1,j+1]<-sum(mapply(Fwithcellvalue,i=i,j=j,a=cells[,2],b=cells[,4],c=cells[,1],d=cells[,3],e=cells[,5]))
>> >
>> > Could you please help me understand how I should
>> change it?
>> >
>> >
>> > Best Regards
>> > Alex
>> >
>> > ______________________________________________
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>> >
>> >
>>
>>
>> -- Andreas Borg
>> Medizinische Informatik
>>
>> UNIVERSITÄTSMEDIZIN
>> der Johannes Gutenberg-Universität
>> Institut für Medizinische Biometrie, Epidemiologie und
>> Informatik
>> Obere Zahlbacher Straße 69, 55131 Mainz
>> www.imbei.uni-mainz.de
>>
>> Telefon +49 (0) 6131 175062
>> E-Mail: borg at imbei.uni-mainz.de
>>
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>
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>