I need to make a dataframe of dummies from survey data where respondents have stated words in several columns in a dataframe. Here is a simplified example to illustrate what I need to do? A single word is here represented by a letter.
id <- c(1:6)
v.1 <- c("a","b","d","e","a","c")
v.2 <- c("b","a","a","a","b","a")
v.3 <- c("e","c","b","b","e","b")
df <- data.frame(id,v.1,v.2,v.3)
> df
id v.1 v.2 v.3
1 1 a b e
2 2 b a c
3 3 d a b
4 4 e a b
5 5 a b e
6 6 c a b
Here is my wanted output?
> print(df.dummy)
id a b c d e
1: 1 1 1 0 0 1
2: 2 1 1 1 0 0
3: 3 1 1 0 1 0
4: 4 1 1 0 0 1
5: 5 1 1 0 0 1
6: 6 1 1 1 0 0
Any ideas?
You can use reshape2:
library(reshape2)
dcast( melt(df,id.var="id"), id ~ value, length)
which gives
id a b c d e
1 1 1 1 0 0 1
2 2 1 1 1 0 0
3 3 1 1 0 1 0
4 4 1 1 0 0 1
5 5 1 1 0 0 1
6 6 1 1 1 0 0
Or use recast to "melt and cast in a single step":
recast(df, id ~ value, id.var = "id", length)
Without using a package, you could do table( rep(df$id,ncol(df)-1), unlist(df[-1]) ).