# Making matrices with zeros and ones

August 30, 2012
By

(This article was first published on Recology - R, and kindly contributed to R-bloggers)

## So I was trying to figure out a fast way to make matrices with randomly allocated 0 or 1 in each cell of the matrix. I reached out on Twitter, and got many responses (thanks tweeps!).

### Here is the solution I came up with. See if you can tell why it would be slow.

``````mm <- matrix(0, 10, 5)
apply(mm, c(1, 2), function(x) sample(c(0, 1), 1))
``````
``````      [,1] [,2] [,3] [,4] [,5]
[1,]    1    0    1    0    1
[2,]    0    0    1    1    1
[3,]    0    0    0    0    1
[4,]    0    1    1    0    1
[5,]    0    1    1    1    1
[6,]    1    0    1    1    1
[7,]    0    1    0    1    0
[8,]    0    0    1    0    1
[9,]    1    0    1    1    1
[10,]    1    0    0    1    1
``````

### Ted Hart (@distribecology) replied first with:

``````matrix(rbinom(10 * 5, 1, 0.5), ncol = 5, nrow = 10)
``````
``````      [,1] [,2] [,3] [,4] [,5]
[1,]    1    1    0    1    1
[2,]    1    0    0    1    0
[3,]    0    1    0    0    0
[4,]    0    0    1    0    0
[5,]    1    0    1    0    0
[6,]    0    0    0    0    1
[7,]    1    0    0    0    0
[8,]    0    1    0    1    0
[9,]    1    1    1    1    0
[10,]    0    1    1    0    0
``````

### Next, David Smith (@revodavid) and Rafael Maia (@hylospar) came up with about the same solution.

``````m <- 10
n <- 5
matrix(sample(0:1, m * n, replace = TRUE), m, n)
``````
``````      [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    0    0    1
[2,]    0    0    0    0    0
[3,]    0    1    1    0    1
[4,]    1    0    0    1    0
[5,]    0    0    0    0    1
[6,]    1    0    1    1    1
[7,]    1    1    1    1    0
[8,]    0    0    0    1    1
[9,]    1    0    0    0    1
[10,]    0    1    0    1    1
``````

### Then there was the solution by Luis Apiolaza (@zentree).

``````m <- 10
n <- 5
round(matrix(runif(m * n), m, n))
``````
``````      [,1] [,2] [,3] [,4] [,5]
[1,]    0    1    1    0    0
[2,]    1    0    1    1    0
[3,]    1    0    1    0    0
[4,]    1    0    0    0    1
[5,]    1    0    1    1    0
[6,]    1    0    0    0    0
[7,]    1    0    0    0    0
[8,]    1    1    1    0    0
[9,]    0    0    0    0    1
[10,]    1    0    0    1    1
``````

### Last, a solution was proposed using `RcppArmadillo`, but I couldn’t get it to work on my machine, but here is the function anyway if someone can.

``````library(inline)
library(RcppArmadillo)
f <- cxxfunction(body = "return wrap(arma::randu(5,10));", plugin = "RcppArmadillo")
``````

### And here is the comparison of system.time for each solution.

``````mm <- matrix(0, 10, 5)
m <- 10
n <- 5

system.time(replicate(1000, apply(mm, c(1, 2), function(x) sample(c(0, 1), 1))))  # @recology_
``````
``````   user  system elapsed
0.470   0.002   0.471
``````
``````system.time(replicate(1000, matrix(rbinom(10 * 5, 1, 0.5), ncol = 5, nrow = 10)))  # @distribecology
``````
``````   user  system elapsed
0.014   0.000   0.015
``````
``````system.time(replicate(1000, matrix(sample(0:1, m * n, replace = TRUE), m, n)))  # @revodavid & @hylospar
``````
``````   user  system elapsed
0.015   0.000   0.014
``````
``````system.time(replicate(1000, round(matrix(runif(m * n), m, n)), ))  # @zentree
``````
``````   user  system elapsed
0.014   0.000   0.014
``````

### Written in Markdown, with help from knitr, and nice knitr highlighting/etc. in in RStudio.

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