mapply to lapply

From: Kenn Konstabel <lebatsnok at gmail.com>
Subject: Re: [R] mapply to lapply
To: "Alaios" <alaios at yahoo.com>
Cc: R-help at r-project.org
Date: Monday, April 18, 2011, 1:06 PM
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