Having trouble converting a dataframe of character vectors to factors

Pleaser re-read ?sapply and pay particular attention to the "simplify" argument.

The following should help explain the issues:
z <- data.frame(a=letters[1:3],b=letters[4:6],stringsAsFactors=FALSE)
sapply(z,class)
a           b
"character" "character"
z1 <- sapply(z,as.factor)
sapply(z1,class)
a           b           c           d           e           f
"character" "character" "character" "character" "character" "character"
z2 <- sapply(z,factor, simplify = FALSE)
sapply(z2,class)
a        b
"factor" "factor"
z3 <- lapply(z,factor)
sapply(z3,class)
a        b
"factor" "factor"
z3
$a
[1] a b c
Levels: a b c

$b
[1] d e f
Levels: d e f

## Note that both z2 and z3 are lists, and would have to be converted
back to data frames.

-- Bert
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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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

Having trouble converting a dataframe of character vectors to factors

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