How to expand a data frame factor column into one column per level in R?

Question

The goal I'm trying to achieve is to take a data frame column which is a factor, create a new column for each level and populate the column with the appropriate value for that level from the original data frame.

Here is a sample. In this case, I want to create a new column for each level of the the.name factor column, like so:

Original dataframe:

symbol        the.name          cn    
SYM1          ABC               1
SYM2          ABC               2
SYM1          DEF               3
SYM2          DEF               4

Resulting dataframe:

symbol       ABC       DEF
SYM1         1         3
SYM2         2         4

How can this be done?

EDIT: I have tried to achieve this using a sapply loop with split by the column and then rbind ing the results. However, I have not gotten it to work and chose not to add it into this question as it would generate noise - I'm pretty sure that method is not correct and can be considerably improved.

Answer 1

This is a job for dcast from the package reshape2 :

> dcast(df, symbol~the.name, value.var="cn")
  symbol ABC DEF
1   SYM1   1   3
2   SYM2   2   4

Answer 2

This is a reshaping task (from long to wide data). The package reshape2 has some great utilities to do this.

txt="symbol        the.name          cn    
      SYM1          ABC               1
      SYM2          ABC               2
      SYM1          DEF               3
      SYM2          DEF               4"

tmp <- read.table(text=txt, header=TRUE)

library(reshape2)
dcast(tmp, symbol ~ the.name)   ## as easy as that

Answer 3

Alternatively, the newish tidyr package provides does this with the "spread" function. Using @ilir's data

> tidyr::spread(tmp, key = the.name, value = cn)
  symbol ABC DEF
1   SYM1   1   3
2   SYM2   2   4