Varying variables in R in a for loop

Question

Hi I'm trying to build a code that tries to do the following:

lists all the files in a folder
extracts the data from each of the excel files (each excel file has multiple sheets and I am using XLConnect package to pull the data from different sheets)
reshape the data into the format that works best for my data analysis

Here is my code

for (i in 1:n) { 
  wb <- loadWorkbook(filelist[i]) 


  assign(paste("field",i,"_reportcontents",sep = ""),
         readWorksheet(wb, sheet="Report Contents"))

  assign(paste("field",i,"_company",sep=""),
         paste("field",i,"_reportcontents[31,3]",sep = ""))
}

The way the above code is set up, the second variable, which is field[i]_company is being set as the string "fieldi_reportcontents[31,3]" rather than the value that is in the dataframe field[i]_reportcontents.

How can I fix the code to achieve the values in the data frame rather than allocation of a string?

@RyanMorton loops don't return things. And OP's `assign` is creating sequentially named objects. — Gregor Thomas, Jan 19 '17 at 18:08
@mvikred If any of the answers provided solved the problem, please mark it as accepted. — Paulo MiraMor, Jan 25 '17 at 01:23

score 1 · Answer 1 · edited May 23 '17 at 11:52

1

Rather than use assign and pasting together variable names, I would use lists.

wb = lapply(filelist, loadWorkbook)
sheets = lapply(wb, readWorksheet, sheet = "Report Contents")
companies = lapply(sheets, "[", 31, 3)

You could easily set the names of the lists, e.g.,

names(sheets) = sprintf("field_%s_reportcontents", seq_along(sheets))

But it isn't clear if this is necessary if you just use good object names with your lists.

See also How to make a list of data frames for more soapboxing about the benefits of lists.

edited May 23 '17 at 11:52

Community

1
1

answered Jan 19 '17 at 18:06

Gregor Thomas

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Although not exactly what i was looking for this code is very elegant and I will make use of it in mine. Thanks !! – mvikred Jan 20 '17 at 08:59

score 0 · Answer 2 · edited May 23 '17 at 12:33

Just assign the sheet being read to a temporary variable. Also, you can replace paste with sep = "" by paste0, it's the same.

for (i in 1:n) { 
  wb <- loadWorkbook(filelist[i]) 

  temp <- readWorksheet(wb, sheet="Report Contents")

  assign(paste0("field",i,"_company"),
         temp)
}

As for why your last assign statement isn't doing what you want, I'll point you to an answer I wrote yesterday. Basically, the value you are trying to assign, paste("field",i,"_reportcontents[31,3]",sep = ""), is just a string. You can use get with a string to use a variable, but in your case you aren't trying to assign a variable either because you are also using the function [, so you would need to parse and evaluate the string you construct. In the end, the list approach is a better way to go.

This works well for me. I've also researched and found mget to be a relevant function here as well. Thanks ! — mvikred, Jan 20 '17 at 09:00

Varying variables in R in a for loop

2 Answers2