How to add a variable to a loop?

Question

I have a dataframe:

  smoke <- matrix(c(51,43,22,92,28,21,68,22,9),ncol=3,byrow=TRUE)
  colnames(smoke) <- c("High","Low","Middle")
  smoke=as.data.frame(smoke);smoke$sit[1]="bit"; smoke$sit[2]="bsa"
  smoke$sit[3]="bu"
    smoke
      High Low Middle sit
   1   51  43     22 bit
   2   92  28     21 bsa
   3   68  22      9  bu

I want apply my simple function:

    myf<- function(c,r){
    x=5*c+r
    write.table(x,paste0("res_", r, "_", c, ".txt"))}
    res=apply(smoke[,c('Low','High')], 1, function(x) myf(x[1],x[2]))

This works fine.output res_51_43.txt .......

Now I just want to add the corresponding names from smoke$sit to output text files. desired output res_bit_51_43.txt .......

    myf<- function(t,c,r){x=5*c+r
    write.table(x,paste0("res_", t, r, "_", c, ".txt"))}
   res=apply(smoke[,c('Low','High','sit')], 1, function(x) myf(x[1],x[2],x[3]))

I got this error:

              Error in 5 * c : non-numeric argument to binary operator

apply converts your data to matrix, and hence your variables to character (as matrices can only hold one data-type). And you would help yourself if you used more descriptive variable names in your function argument. — Heroka
– Heroka, Commented Nov 27, 2015 at 16:44
You could use lapply on a split dataframe (list can have multiple data-types in them) — Heroka
– Heroka, Commented Nov 27, 2015 at 17:10

Heroka · Accepted Answer · 2015-11-27 17:14:46Z

1

Here's an example using lapply and split. Note: I've modified your function to return a filename.

myf<- function(c,r,t){
  x=5*c+r
  myfile <- paste0("res_", t, r, "_", c, ".txt")
  return(myfile)
}

res=lapply(split(smoke[,c('Low','High','sit')],1:nrow(smoke)), 
    FUN=function(x) myf(c=x[1],r=x[2],t=x[3]))
> res
$`1`
[1] "res_bit51_43.txt"

$`2`
[1] "res_bsa92_28.txt"

$`3`
[1] "res_bu68_22.txt"

answered Nov 27, 2015 at 17:14

Heroka

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3 Comments

Heroka Over a year ago

I'm not generating text files on my machine. What about the provided code is giving you problems?

temor Over a year ago

Yes It worked but in the output text file, it does not return 'x(the name I provided)'. 'my function: "x" "Low" 266'______'yourfunction :"Low" "1" 266'

Heroka Over a year ago

I couldn't really figure out your variable mappings, as you switch them around a lot. The issue of generating filenames and the error you got using 'apply' seems solved to me. Maybe try myf(c=x[2], r=x[1], t=x[3]) inside function(x)?

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