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## beginner's loop issue

 Dear All, I hope you don't mind helping me with this small issue. I haven't been using R in years and I'm trying to fill in a matrix with the output of a function (I'm probably using the Matlab logic here and it's not working). Here is my code: for (i in 1:length(input)){   out[i,1:3] <- MyFunction(input[i,1],input[i,2], input[i,3])     out[i,4:6] <- MyFunction(input[i,5],input[i,7], input[i,6])       out[i,7:9] <- MyFunction(input[i,8],input[i,10], input[i,9]) } 'input' is a matrix > dim(input)  46 10 and each raw corresponds to a different subject. The error I get here is Error in out[i, 1:3] <- get.vaTer(input[i, 2], input[i, 4], input[i, 3],  :   object 'out' not foundSo I wonder, what's wrong in the assignment to the variable out? Should I define the variable before the loop? Thanks for your help Best Ale
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## Re: beginner's loop issue

 Yes, the short answer is that you need to define out before running the loop. The most effective way to do so will be to set up a matrix with the exact right dimensions (if you know them up front); something like out <- matrix(NA, nrow = length(input), ncol = 9) Michael On Tue, Mar 13, 2012 at 12:27 PM, aledanda <[hidden email]> wrote: > Dear All, > > I hope you don't mind helping me with this small issue. I haven't been using > R in years and I'm trying to fill in a matrix > with the output of a function (I'm probably using the Matlab logic here and > it's not working). > Here is my code: > > for (i in 1:length(input)){ >  out[i,1:3] <- MyFunction(input[i,1],input[i,2], input[i,3]) >    out[i,4:6] <- MyFunction(input[i,5],input[i,7], input[i,6]) >      out[i,7:9] <- MyFunction(input[i,8],input[i,10], input[i,9]) > } > > 'input' is a matrix >> dim(input) >  46 10 > > and each raw corresponds to a different subject. > The error I get here is > > /Error in out[i, 1:3] <- get.vaTer(input[i, 2], input[i, 4], input[i, 3],  : >  object 'out' not found/ > > So I wonder, what's wrong in the assignment to the variable out? > Should I define the variable before the loop? > > Thanks for your help > Best > > Ale > > -- > View this message in context: http://r.789695.n4.nabble.com/beginner-s-loop-issue-tp4469514p4469514.html> Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > [hidden email] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html> and provide commented, minimal, self-contained, reproducible code. ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: beginner's loop issue

 In reply to this post by aledanda On Tue, Mar 13, 2012 at 11:27 AM, aledanda <[hidden email]> wrote: > Dear All, > > I hope you don't mind helping me with this small issue. I haven't been using > R in years and I'm trying to fill in a matrix > with the output of a function (I'm probably using the Matlab logic here and > it's not working). > Here is my code: > > for (i in 1:length(input)){ >  out[i,1:3] <- MyFunction(input[i,1],input[i,2], input[i,3]) >    out[i,4:6] <- MyFunction(input[i,5],input[i,7], input[i,6]) >      out[i,7:9] <- MyFunction(input[i,8],input[i,10], input[i,9]) > } > > 'input' is a matrix >> dim(input) >  46 10 > > and each raw corresponds to a different subject. > The error I get here is > > /Error in out[i, 1:3] <- get.vaTer(input[i, 2], input[i, 4], input[i, 3],  : >  object 'out' not found/ out has to exist first, as previous commenter said. Furthermore, suggestions: Consider making MyFunction accept a vector of 3 arguments, rather than separate arguments. Consider making out 3 columns, as in out <- matrix(0, nrow=N, ncol=3) for(i ...){ out[i,1:3] <- MyFunction(input[i,1:3]) out[i,1:3] <- MyFunction(input[i,4:6]) out[i,1:3] <- MyFunction(input[i,7:9]) } If you could re-shape your input "thing" as a list with one element that needs to go into MyFunction, this could get easier still: lapply(input, MyFunction)  or if input were an array with 3 columns, you could revise MyFuntion to accept a 3-vector. apply(input, 1, MyFunction) Hardly ever in R does one need to specify inputs as you have done in your example. pj -- Paul E. Johnson Professor, Political Science    Assoc. Director 1541 Lilac Lane, Room 504     Center for Research Methods University of Kansas               University of Kansas http://pj.freefaculty.org            http://quant.ku.edu______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: beginner's loop issue

 Thank you all for your helpful comments! I solved my problem by creating an empty matrix before the loop and adjusting the loop itself, this is the code: size <- dim(input) out <- matrix('',nrow =size, ncol =  9) for (i in 1:nrow(input)) {     out[i,1:3] <- unlist(MyFunction(input[i,1],input[i,2], input[i,3])     out[i,4:6] <- unlist(MyFunction(input[i,5],input[i,7], input[i,6])       out[i,7:9] <- unlist(MyFunction(input[i,8],input[i,10], input[i,9]) } It's probably not the most efficient way of doing it but it gives me the desired output matrix... Thanks for pointing me to this pdf R inferno pdf, I had an old version of it.. I'm, starting to use R again after long time and this is a very useful guide! All the best Ale