[R] Sampling letters

[Doran, Harold]

I have a binary matrix of size N x 300. I then create the following:

> set.seed(1234)
> (key_file <- sample(letters[1:4], 300, replace=TRUE))
  [1] "a" "c" "c" "c" "d" "c" "a" "a" "c" "c" "c" "c" "b" "d" "b" "d"
"b" "b" "a" "a" "b" "b" "a"
 [24] "a" "a" "d" "c" "d" "d" "a" "b" "b" "b" "c" "a" "d" "a" "b" "d"
"d" "c" "c" "b" "c" "b" "c"
 [47] "c" "b" "a" "d" "a" "b" "c" "c" "a" "c" "b" "d" "a" "d" "d" "a"
"b" "a" "a" "c" "b" "c" "a"
 [70] "c" "a" "d" "a" "d" "a" "c" "b" "a" "b" "c" "d" "b" "a" "c" "a"
"d" "b" "b" "a" "d" "a" "d"
 [93] "a" "a" "a" "c" "b" "a" "b" "c" "a" "c" "b" "a" "a" "b" "a" "a"
"b" "a" "c" "a" "d" "a" "a"
[116] "d" "d" "b" "a" "d" "c" "d" "d" "d" "b" "b" "b" "c" "b" "b" "d"
"c" "a" "b" "d" "b" "d" "c"
[139] "c" "d" "c" "d" "b" "b" "b" "c" "c" "c" "d" "c" "b" "a" "a" "d"
"a" "d" "c" "d" "b" "c" "b"
[162] "c" "b" "a" "a" "c" "b" "a" "d" "b" "d" "c" "c" "b" "b" "d" "b"
"c" "a" "b" "b" "b" "c" "a"
[185] "d" "a" "d" "c" "b" "c" "c" "d" "a" "d" "d" "d" "d" "c" "d" "c"
"c" "c" "b" "d" "c" "c" "b"
[208] "b" "a" "d" "c" "b" "a" "d" "c" "d" "c" "c" "b" "d" "b" "a" "b"
"b" "a" "b" "d" "b" "c" "b"
[231] "d" "c" "a" "d" "c" "a" "c" "b" "b" "d" "b" "a" "a" "c" "d" "b"
"d" "c" "d" "d" "c" "c" "b"
[254] "b" "a" "c" "b" "a" "c" "c" "d" "a" "c" "b" "a" "a" "c" "a" "a"
"c" "b" "d" "b" "d" "a" "c"
[277] "d" "c" "b" "b" "b" "b" "d" "d" "c" "b" "b" "b" "c" "d" "c" "b"
"d" "a" "c" "d" "c" "a" "c"
[300] "b"

I now replace all 1's in column 1 with key_file[1], I replace all 1's in
column 2 with key_file[2] and so on through column 300. This part is
simple.

Now, I want to replace the 0's in column 1 with either b,c, or d, but
not with an a since that was used to replace the 1's. For column 2 I
want to replace all 0's with either a,b, or d but not with c since that
was used to replace the 1's.

However, I do not want all 0's in column 1 to be the same letter. That
is, I would not want them all to be replaced with a 'b'. Rather, I want
to randomly recode the 0's as either b,c, or d. So, some 0's will be
recoded as b, some as c, and some as d.

If I were replacing the zeros with the same letter, this would be a
simple ifelse command. But, because I want randomness I'm not sure how I
can do this other than a costly loop than goes through the data matrix
cell-by-cell and does some replacement. That would be fine, but very
time consuming.

Does anyone have thoughts on how else I could tackle this?

Harold