Question

I want to paste variables in the logical expression that I am using to subset data, but the subset function does not see them as column names when pasted (either with ot without quotes).

I have a dataframe with columns named col1, col2 etc. I want to subset for the rows in which colx < 0.05

This DOES work:

subsetdata<-subset(dataframe, col1<0.05)

subsetdata<-subset(dataframe, col2<0.05)

This does NOT work:

for (k in 1:2){
subsetdata<-subset(dataframe, paste("col",k,sep="")<0.05)
}

for (k in 1:2){
subsetdata<-subset(dataframe, noquote(paste("col",k,sep=""))<0.05)
}

I can’t find the answer; any suggestions?

Answer 1

Here are a couple of options that are closer to the Jasper’s approach. First, you could define the column name as a separate variable and then use it to select the variable from the data.frame as if it were a list (since a data.frame is basically a list):

for(k in 1:2){
  colname <- paste("col",k,sep="")
  subsetdata <- dataframe[dataframe[[colname]] < 0.05, ]
}

Or you could refer to the column name as such:

  subsetdata <- dataframe[dataframe[colname,] < 0.05, ]

Finally, you could use subset, although you need to provide a logical expression (as pointed out by Joshua Ulrich):

  subsetdata <- subset(dataframe, eval(substitute(x < 0.05, list(x = as.name(colname)))))