Convert a dataframe to presence absence matrix

Question

I have a table which has unequal number of element in string format

File1 A  B  C
File2 A  B  D
File3 E  F

I want to convert into a format

Answer 1

One possibility:

library(reshape2)
df2 <- melt(df, id.var = "V1")
with(df2, table(V1, value))

#         value
# V1      A B C D E F
#   File1 1 1 1 0 0 0
#   File2 1 1 0 1 0 0
#   File3 0 0 0 0 1 1