CODEWITHSUNDEEP
riteration
Ross Clark
Ross Clark

Reputation: 21

R - iterating over rows with if statements

I am slowly teaching myself R, with a very basic background in programming. Producing plots etc. is relatively straightforward, but I am currently working on a small piece of code, with the intention of building a larger script for making processing of commercial lab results less onerous - these are typically issued in fairly disorganised CSV files, with a mixture of different units of concentration.

So, I am trying to produce a block of code which iterates through the rows of a CSV file containing four column headings: "Analyte", "Unit", "LOD", and "Concentration". I intend for my code to check which unit is being used for each analyte, and if it is mg/l, convert the concentration to ug/l for this analyte:

input_file <- read.csv(file="test.csv", header = TRUE,sep = ",")


apply(input_file, 1, function(row) {
  if (input_file$Unit == "mg/l"){
    input_file$Concentration <- input_file$Concentration*1000
  }
  }
  )

print(input_file)

When I run this code (I am using Rstudio), I get the following error message: In if (input_file$Unit == "mg/l") { : the condition has length > 1 and only the first element will be used. I cannot find a solution to this, and my limited knowledge of programming jargon seems to be hindering this. Any ideas? Any suggestions, hints or resources would be much appreciated.

Upvotes: 1

Views: 65

Answers (1)

Tim Biegeleisen
Tim Biegeleisen

Reputation: 521053

I believe this is what you were intending to do:

apply(input_file, 1, function(row) {
    if (row$Unit == "mg/l"){
        row$Concentration <- row$Concentration*1000
    }
})

The temporary variable row represents each row of the input file, and it is this which you mean to modify.

Here is a more efficient way to do this:

input_file[input_file$Unit == "mg/l", "Concentration"] <-
    input_file[input_file$Unit == "mg/l", "Concentration"]*1000

Upvotes: 1

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