[R] Having trouble converting a dataframe of character vectors to factors

[William Dunlap]

> scs2<-data.frame(lapply(scs2, factor))

Calling data.frame() on the output of lapply() can result in changing column names
and will drop attributes that the input data.frame may have had.  I prefer to modify
the original data.frame instead of making a new one from scratch to avoid these problems.

Also, calling factor() on a factor will drop any unused levels, which you may not want
to do.  Calling as.factor will not.

Compare the following three methods

  f1 <- function (dataFrame) {
      dataFrame[] <- lapply(dataFrame, factor)
      dataFrame
  }
  f2 <- function (dataFrame) {
      dataFrame[] <- lapply(dataFrame, as.factor)
      dataFrame
  }
  f3 <- function (dataFrame) {
      data.frame(lapply(dataFrame, factor))
  }

on the following data.frame
  x <- data.frame(stringsAsFactors=FALSE, check.names=FALSE,
               "No/Yes" = factor(c("Yes","Yes","Yes"), levels=c("No","Yes")),
               "Size" = ordered(c("Small","Large","Medium"), levels=c("Small","Medium","Large")),
               "Name" = c("Adam","Bill","Chuck"))
  attr(x, "Date") <- as.POSIXlt("2013-02-21")


  > str(x)
  'data.frame':   3 obs. of  3 variables:
   $ No/Yes: Factor w/ 2 levels "No","Yes": 2 2 2
   $ Size  : Ord.factor w/ 3 levels "Small"<"Medium"<..: 1 3 2
   $ Name  : chr  "Adam" "Bill" "Chuck"
   - attr(*, "Date")= POSIXlt, format: "2013-02-21"

  > str(f1(x)) # drops unused levels
  'data.frame':   3 obs. of  3 variables:
   $ No/Yes: Factor w/ 1 level "Yes": 1 1 1
   $ Size  : Ord.factor w/ 3 levels "Small"<"Medium"<..: 1 3 2
   $ Name  : Factor w/ 3 levels "Adam","Bill",..: 1 2 3
   - attr(*, "Date")= POSIXlt, format: "2013-02-21"
  > str(f2(x))
  'data.frame':   3 obs. of  3 variables:
   $ No/Yes: Factor w/ 2 levels "No","Yes": 2 2 2
   $ Size  : Ord.factor w/ 3 levels "Small"<"Medium"<..: 1 3 2
   $ Name  : Factor w/ 3 levels "Adam","Bill",..: 1 2 3
   - attr(*, "Date")= POSIXlt, format: "2013-02-21"
  > str(f3(x)) # mangles column names, drops unused levels, drops Date attribute
  'data.frame':   3 obs. of  3 variables:
   $ No.Yes: Factor w/ 1 level "Yes": 1 1 1
   $ Size  : Ord.factor w/ 3 levels "Small"<"Medium"<..: 1 3 2
   $ Name  : Factor w/ 3 levels "Adam","Bill",..: 1 2 3

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Mark Lamias
> Sent: Wednesday, February 20, 2013 6:51 PM
> To: Daniel Lopez; R help (r-help at r-project.org)
> Subject: Re: [R] Having trouble converting a dataframe of character vectors to factors
> 
> How about this?
> 
> scs2<-data.frame(lapply(scs2, factor))
> 
> 
> 
> 
> ________________________________
>  From: "Lopez, Dan" <lopez235 at llnl.gov>
> To: "R help (r-help at r-project.org)" <r-help at r-project.org>
> Sent: Wednesday, February 20, 2013 7:09 PM
> Subject: [R] Having trouble converting a dataframe of character vectors to factors
> 
> R Experts,
> 
> I have a dataframe made up of character vectors--these are results from survey
> questions. I need to convert them to factors.
> 
> I tried the following which did not work:
> scs2<-sapply(scs2,as.factor)
> also this didn't work:
> scs2<-sapply(scs2,function(x) as.factor(x))
> 
> After doing either of above I end up with
> >str(scs2)
> 
> chr [1:10, 1:10] "very important" "very important" "very important" "very important" ...
> 
> - attr(*, "dimnames")=List of 2
> 
>   ..$ : NULL
> 
>   ..$ : chr [1:10] "Q1_1" "Q1_2" "Q1_3" "Q1_4" ...
> 
> >class(scs2)
> "matrix"
> 
> But when I do it one at a time it works:
> scs2$Q1_1<-as.factor(scs2$Q1_1)
> scs2$Q1_2<- as.factor(scs2$Q1_2)
> 
> What am I doing wrong?  How do I accomplish this with sapply or similar function?
> 
> Data for reproducibility:
> 
> 
> scs2<-structure(list(Q1_1 = c("very important", "very important", "very important",
> 
> "very important", "very important", "very important", "very important",
> 
> "somewhat important", "important", "very important"), Q1_2 = c("important",
> 
> "somewhat important", "very important", "important", "important",
> 
> "very important", "somewhat important", "somewhat important",
> 
> "very important", "very important"), Q1_3 = c("very important",
> 
> "important", "very important", "very important", "important",
> 
> "very important", "very important", "somewhat important", "not important",
> 
> "important"), Q1_4 = c("very important", "important", "very important",
> 
> "very important", "important", "important", "important", "very important",
> 
> "somewhat important", "important"), Q1_5 = c("very important",
> 
> "not important", "important", "very important", "not important",
> 
> "important", "somewhat important", "important", "somewhat important",
> 
> "not important"), Q1_6 = c("very important", "not important",
> 
> "important", "very important", "somewhat important", "very important",
> 
> "very important", "very important", "important", "important"),
> 
>     Q1_7 = c("very important", "somewhat important", "important",
> 
>     "somewhat important", "important", "important", "very important",
> 
>     "very important", "somewhat important", "not important"),
> 
>     Q2 = c("Somewhat", "Very Much", "Somewhat", "Very Much",
> 
>     "Very Much", "Very Much", "Very Much", "Very Much", "Very Much",
> 
>     "Very Much"), Q3 = c("yes", "yes", "yes", "yes", "yes", "yes",
> 
>     "yes", "yes", "yes", "yes"), Q4 = c("None", "None", "None",
> 
>     "None", "Confirmed Field of Study", "Confirmed Field of Study",
> 
>     "Confirmed Field of Study", "None", "None", "None")), .Names = c("Q1_1",
> 
> "Q1_2", "Q1_3", "Q1_4", "Q1_5", "Q1_6", "Q1_7", "Q2", "Q3", "Q4"
> 
> ), row.names = c(78L, 46L, 80L, 196L, 188L, 197L, 39L, 195L,
> 
> 172L, 110L), class = "data.frame")
> 
> 
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> 
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