Table by row with R

Question

I would like to tabulate by row within a data frame. I can obtain adequate results using table within apply in the following example:

Answer 1

Here's a table solution:

table(
    rep(rownames(df.1),5),
    unlist(df.1[,4:8]),
    useNA="ifany")

This gives

    0 1 2 10 20 200 <NA>
  1 3 1 1  0  0   0    0
  2 0 0 0  3  1   0    1
  3 0 0 0  0  0   3    2
  4 0 0 0  0  0   0    5

...and for your df.2:

    0 1 2 <NA>
  1 5 0 0    0
  2 0 5 0    0
  3 0 0 5    0
  4 0 0 0    5

Well, this is a solution unless you really like having a list of tables for some reason.

Answer 2

I think the problem is stated in applys help:

... If n equals 1, apply returns a vector if MARGIN has length 1 and an array of dimension dim(X)[MARGIN] otherwise ...

The inconsistencies of the return values of base R's apply family is the reason why I shifted completely to plyrs **ply functions. So this works as desired:

library(plyr)
alply( df.2[ 4:8 ], 1, function(x) table( unlist(x), useNA = "ifany" ) )

Answer 3

You can use lapply to systematically output a list. You would have to loop over the row indices:

sub.df <- as.matrix(df.2[grepl("year", names(df.2))])
lapply(seq_len(nrow(sub.df)), 
       function(i)table(sub.df[i, ], useNA = "ifany"))

Answer 4

Protect the result by wrapping with list:

apply(tdf.2[4:nrow(tdf.2),1:nrow(df.2)], 2, 
              function(x) {list(table(x, useNA = "ifany")) })