Populating an array using a FOR loop and a function

Question

I was expecting that the following code would populate E with random 1's and 0's, but that does not happen. I cannot figure out why.

Pkg.add("StatsBase")
using StatsBase

function randomSample(items,weights)
    sample(items, Weights(weights))
end



n = 10
periods = 100

p = [ones(n,periods)*0.5]
E = fill(NaN, (n,periods))

for i in 1:periods
    for ii in 1:n
        E(ii,i) = randomSample([1 0],[(p(ii,i)), 1 - p(ii,i)])
    end
end
E

Unlike MATLAB, indexing is done with brackets in Julia not with parentheses. Be careful with the brackets, though, [ones(5, 10)] will give you an Array of Array(s). In MATLAB, however, it makes no difference to add as many surrounding brackets as possible: the result will be just a matrix. — hckr
– hckr, Commented May 6, 2019 at 22:03
Since you are already using fill to initialize E, why not do the same with p:? That is, p = fill(0.5, (n, periods)). This is more efficient (and reasonable) than first creating a matrix of ones, and then creating a second matrix by multiplying the first one with 0.5. — DNF
– DNF, Commented May 7, 2019 at 6:37

Bogumił Kamiński · Accepted Answer · 2019-05-06 21:57:16Z

2

The statement:

E(ii,i) = randomSample([1 0],[(p(ii,i)), 1 - p(ii,i)])

defines a local function E and is not an assignment operation to a matrix E. Use

E[ii,i] = randomSample([1, 0],[p[ii,i], 1 - p[ii,i]])

(I have fixed additional errors in your code so please check out the differences)

and for it to run you should also write:

p = ones(n,periods)*0.5

answered May 6, 2019 at 21:57

Bogumił Kamiński

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