Question

I’m trying to loop over variables (I’m still struggling to get my head around the apply() family, one day soon) and construct the variable names that I wish to obtain the labels for.

A simplified example is perhaps easiest…

library(Hmisc)
t <- data.frame(matrix(1:100, 10))
label(t$X1)  <- "This is my first variable"
label(t$X2)  <- "This is my second variable"
label(t$X3)  <- "This is my third variable"
label(t$X4)  <- "This is my fourth variable"
label(t$X5)  <- "This is my fifth variable"
label(t$X6)  <- "This is my sixth variable"
label(t$X7)  <- "This is my seventh variable"
label(t$X8)  <- "This is my eighth variable"
label(t$X9)  <- "This is my ninth variable"
label(t$X10) <- "This is my tenth variable"
for(x in 1:10){
  my.label <- label(paste("t$X", x, sep=""))
  print(my.label)
}

When run this gives….

[1] ""
[1] ""
[1] ""
[1] ""
[1] ""
[1] ""
[1] ""
[1] ""
[1] ""
[1] ""

When I’m expecting to see

[1] "This is my first variable"
[1] "This is my second variable"
[1] "This is my third variable"
[1] "This is my fourth variable"
[1] "This is my fifth variable"
[1] "This is my sixth variable"
[1] "This is my seventh variable"
[1] "This is my eighth variable"
[1] "This is my ninth variable"
[1] "This is my tenth variable"

I know the paste() function is working correctly because…

for(x in 1:10){
  print(paste("t$X", x, sep=""))
}
[1] "X$1"
[1] "X$2"
[1] "X$3"
[1] "X$4"
[1] "X$5"
[1] "X$6"
[1] "X$7"
[1] "X$8"
[1] "X$9"
[1] "X$10"

I’m stumped, I’ve tried placing the paste() within eval() as in…

for(x in 1:10){
  my.label <- label(eval(paste("t$X", x, sep="")))
  print(my.label)
}

…but no joy. It seems such a simple thing, and I’ve tried searching for solutions but clearly aren’t describing it properly with phrases I’m trying hence asking here.

Insights and pointers very much appreciated.

Thanks,

slackline

EDIT : The above is a simplified example to illustrate what I am trying to achieve which is a bit more complex, currently my code looks like…

for(type1 in c("bouldering", "routes")){
  if(type1 == "bouldering"){
    part   <- c("indoors", "outdoors")
    xlabel <- "Grade (Fontainebleau)"
  }
  else if(type1 == "routes"){
    part <- c("onsight", "redpoint")
    xlabel <- "Grade (French Sports)"
  }
  for(type2 in part){
    for(training in c("pullup.rep", "pullup.weight", "hang.time", "hang.size", "bench.press", "bench.press.scaled", "dead.lift", "dead.lift.scaled", "front.lever", "height", "weight", "bmi")){
      ### Obtain the current variables label for using in the graph
      ylabel <- label(paste("clean.data", training, sep="$"))
      ### Paste the bouldering/routes together with indoors/
      ### outdoors or onsight/redpoint so variables and files can be constructed
      file.stub <- paste(type1, type2, sep="-")
      metric    <- paste(type1, type2, sep=".")
      file.out  <- paste("latex/figures/", gsub("\\.", "-", training) , "-", file.stub, ".png", sep="")
      png(file.out, width=1024, height=768)
      t <- qplot(metric, training,
                 data     = clean.data,
                 geom     = "boxplot",
                 fill     = factor(metric),
                 xlab     = xlabel,
                 ylab     = ylabel)
      t + opts(legend.position = "none")
      dev.off()
    }
  }
}

So currently I don’t get a label, and I don’t get graphs because the commands (label() and qplot()) don’t know that I’m referring to column names with the data frame clean.data

Answer 1

This will work:

for(x in 1:10){
  my.label <- label(t[paste("X", x, sep="")])
  print(my.label)
}

This would be simpler:

label(t)