how to convert a matrix of values into a binary matrix

Question

I'd like to convert a matrix of values into a matrix of 'bits'.

I have been looking for solutions and found this, which seems to be part of a solution. I'll try to explain what I am looking for. I have a matrix like

> x<-matrix(1:20,5,4)
> x
     [,1] [,2] [,3] [,4]
[1,]    1    6   11   16
[2,]    2    7   12   17
[3,]    3    8   13   18
[4,]    4    9   14   19
[5,]    5   10   15   20

which I would like to convert into

     1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
  1  1 0 0 0 0 1 0 0 0  0  1  0  0  0  0  1  0  0  0  0
  2  0 1 0 0 0 0 1 0 0  0  0  1  0  0  0  0  1  0  0  0
  3  0 0 1 0 0 0 0 1 0  0  0  0  1  0  0  0  0  1  0  0
  4  0 0 0 1 0 0 0 0 1  0  0  0  0  1  0  0  0  0  1  0
  5  0 0 0 0 1 0 0 0 0  1  0  0  0  0  1  0  0  0  0  1

so for each value in the row a "1" in the corresponding column.

If I use

> table(sequence(length(x)),t(x))

     1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
  1  1 0 0 0 0 0 0 0 0  0  0  0  0  0  0  0  0  0  0  0
  2  0 0 0 0 0 1 0 0 0  0  0  0  0  0  0  0  0  0  0  0
  3  0 0 0 0 0 0 0 0 0  0  1  0  0  0  0  0  0  0  0  0
  4  0 0 0 0 0 0 0 0 0  0  0  0  0  0  0  1  0  0  0  0
  5  0 1 0 0 0 0 0 0 0  0  0  0  0  0  0  0  0  0  0  0
  6  0 0 0 0 0 0 1 0 0  0  0  0  0  0  0  0  0  0  0  0
  7  0 0 0 0 0 0 0 0 0  0  0  1  0  0  0  0  0  0  0  0
  8  0 0 0 0 0 0 0 0 0  0  0  0  0  0  0  0  1  0  0  0
  9  0 0 1 0 0 0 0 0 0  0  0  0  0  0  0  0  0  0  0  0
  10 0 0 0 0 0 0 0 1 0  0  0  0  0  0  0  0  0  0  0  0
  11 0 0 0 0 0 0 0 0 0  0  0  0  1  0  0  0  0  0  0  0
  12 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0  0  0  1  0  0
  13 0 0 0 1 0 0 0 0 0  0  0  0  0  0  0  0  0  0  0  0
  14 0 0 0 0 0 0 0 0 1  0  0  0  0  0  0  0  0  0  0  0
  15 0 0 0 0 0 0 0 0 0  0  0  0  0  1  0  0  0  0  0  0
  16 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0  0  0  0  1  0
  17 0 0 0 0 1 0 0 0 0  0  0  0  0  0  0  0  0  0  0  0
  18 0 0 0 0 0 0 0 0 0  1  0  0  0  0  0  0  0  0  0  0
  19 0 0 0 0 0 0 0 0 0  0  0  0  0  0  1  0  0  0  0  0
  20 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0  0  0  0  0  1

this is close to what I am looking for, but returns a line for each value.

I would only need to consolidate all values from one row into one row. Because a

> table(x)
x
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 
 1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1

gives alls values of the whole table, so what do I need to do to get the values per row.

What if there are two equal integers in the same row? – Julius Vainora Jul 17 '16 at 16:01 — Julius Vainora, Jul 17 '16 at 16:01
That conceptionally not the case. – Kurt Ludikovsky Jul 17 '16 at 16:57 — Kurt Ludikovsky, Jul 17 '16 at 16:57

score 4 · Answer 1 · answered Jul 17 '16 at 15:47

4

    bit_x = matrix(0, nrow = nrow(x), ncol = max(x))
    for (i in 1:nrow(x)) {bit_x[i,x[i,]] = 1}

answered Jul 17 '16 at 15:47

jac

620
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Julius Vainora · Answer 2 · 2016-07-17T16:15:41.380

Let

(x <- matrix(c(1, 3), 2, 2))
     [,1] [,2]
[1,]    1    1
[2,]    3    3

One approach would be

M <- matrix(0, nrow(x), max(x))
M[cbind(c(row(x)), c(x))] <- 1
M
#      [,1] [,2] [,3]
# [1,]    1    0    0
# [2,]    0    0    1

In one line:

replace(matrix(0, nrow(x), max(x)), cbind(c(row(x)), c(x)), 1).

Following your approach, and similarly to @Psidom's suggestion:

table(rep(1:nrow(x), ncol(x)), x)
#    x
#     1 3
#   1 2 0
#   2 0 2

Psidom · Accepted Answer · 2016-07-17T16:14:20.940

4

Here is another option using table() function:

table(row(x), x)
#   x
#    1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
#  1 1 0 0 0 0 1 0 0 0  0  1  0  0  0  0  1  0  0  0  0
#  2 0 1 0 0 0 0 1 0 0  0  0  1  0  0  0  0  1  0  0  0
#  3 0 0 1 0 0 0 0 1 0  0  0  0  1  0  0  0  0  1  0  0
#  4 0 0 0 1 0 0 0 0 1  0  0  0  0  1  0  0  0  0  1  0
#  5 0 0 0 0 1 0 0 0 0  1  0  0  0  0  1  0  0  0  0  1

edited Jul 17 '16 at 16:14

answered Jul 17 '16 at 15:59

Psidom

209,562
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score 2 · Answer 4 · edited Jul 17 '16 at 20:36

We can use the reshape2 package.

library(reshape2)
# At first we make the matrix you provided 
x <- matrix(1:20, 5, 4)
# then melt it based on first column
da <- melt(x, id.var = 1)
# then cast it
dat <- dcast(da, Var1 ~ value, fill = 0, fun.aggregate = length)

which gives us this

  Var1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
1    1 1 0 0 0 0 1 0 0 0  0  1  0  0  0  0  1  0  0  0  0
2    2 0 1 0 0 0 0 1 0 0  0  0  1  0  0  0  0  1  0  0  0
3    3 0 0 1 0 0 0 0 1 0  0  0  0  1  0  0  0  0  1  0  0
4    4 0 0 0 1 0 0 0 0 1  0  0  0  0  1  0  0  0  0  1  0
5    5 0 0 0 0 1 0 0 0 0  1  0  0  0  0  1  0  0  0  0  1

how to convert a matrix of values into a binary matrix

4 Answers4