[R] Applying variable labels across a data frame

[Muenchen, Robert A (Bob)]

Hi All,

I'm working on a class example that demonstrates one way to deal with
factors and their labels. I create a function called myLabeler and apply
it with lapply. It works on the whole data frame when I subscript it as
in lapply( myQFvars[ ,myQFnames ], myLabeler ) but does not work if I
leave the [] subscripts off. I would appreciate it if anyone could tell
me why. The program below works up until the final two statements.

Thanks,
Bob


# Assigning factor labels to potentially lots of vars.

mystring<-
("id,workshop,gender,q1,q2,q3,q4
 1,1,f,1,1,5,1
 2,2,f,2,1,4,1
 3,1,f,2,2,4,3
 4,2,f,3,1, ,3
 5,1,m,4,5,2,4
 6,2,m,5,4,5,5
 7,1,m,5,3,4,4
 8,2,m,4,5,5,9")

mydata<-read.table(textConnection(mystring),
   header=TRUE,sep=",",row.names="id",na.strings="9")
print(mydata)

# Create copies of q variables to use as factors
# so we can count them.
myQlevels <- c(1,2,3,4,5)
myQlabels <- c("Strongly Disagree",
               "Disagree",
               "Neutral",
               "Agree",
               "Strongly Agree")
print(myQlevels)
print(myQlabels)

# Generate two sets of var names to use.
myQnames  <-   paste( "q",  1:4, sep="")
myQFnames <- paste( "qf", 1:4, sep="")
print(myQnames) #The original names.
print(myQFnames)  #The names for new factor variables.

# Extract the q variables to a separate data frame.
myQFvars <- mydata[ ,myQnames]
print(myQFvars)

# Rename all the variables with F for Factor.
colnames(myQFvars) <- myQFnames
print(myQFvars)

# Create a function to apply the labels to lots of variables.
myLabeler <- function(x) { factor(x, myQlevels, myQlabels) }

# Here's how to use the function on one variable.
summary( myLabeler(myQFvars["qf1"]) )

#Apply it to all the variables. This method works.
myQFvars[ ,myQFnames] <- lapply( myQFvars[ ,myQFnames ], myLabeler )
summary(myQFvars) #Here are the results I wanted.

# This is the same as above but using the unsubscripted
# data frame name. It does not work.
myTest <- lapply( myQFvars, myLabeler )
summary(myTest) #I'm not sure what these results are.

=========================================================
  Bob Muenchen (pronounced Min'-chen), Manager  
  Statistical Consulting Center
  U of TN Office of Information Technology
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