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multidimensional-arrayjulia
Ben Hamner
Ben Hamner

Reputation: 4735

Constructing a multi-dimensional array in Julia

In MATLAB, the following syntax can be used to create 1-d matrix a and 2-d matrix b:

a = [2,3]
b = [2,3;4,5]

In Julia, constructing the 1-d array a using the same syntax works. However, constructing the 2-d array b using the same syntax fails.

Defining b as follows works:

b = cat(2,[2,4],[3,5])

Is there a syntactical shortcut for explicitly defining 2-d arrays in Julia? If so, what is it?

Upvotes: 5

Views: 4396

Answers (4)

James Burgess
James Burgess

Reputation: 497

As of Julia 0.6 depending on which dimension you seek, you could use

# hcat
b = [[2, 3] [4, 5]]
2×2 Array{Int64,2}: [2 4; 3 5]

# vcat
c = [[2 3] ; [4 5]]
2×2 Array{Int64,2}: [2 3; 4 5]

Upvotes: 0

waldyrious
waldyrious

Reputation: 3844

You're likely looking for this:

a = [2,3]
b = [2 3;4 5]

Here's the relevant paragraph from the "Major Differences From MATLAB" section of the Julia docs:

Concatenating scalars and arrays with the syntax [x,y,z] concatenates in the first dimension (“vertically”). For the second dimension (“horizontally”), use spaces as in [x y z]. To construct block matrices (concatenating in the first two dimensions), the syntax [a b; c d] is used to avoid confusion.

Upvotes: 6

tholy
tholy

Reputation: 12179

You can also say [1 2; 3 4], which gives the same result as in Matlab.

Upvotes: 5

Ben Hamner
Ben Hamner

Reputation: 4735

The following syntax works (but is not as terse as the MATLAB equivalent):

b = [[2 3],[4 5]]

Upvotes: 1

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