Reading Collections
Tuples
Immutable, indexable, possibly heterogeneous collections of elements:
typeof((2, 4, 1.0, "test"))
(2, 4, 1.0, "test")[2]Named tuples
Tuples can have named components:
typeof((a=2, b=4, c=1.0, d="test"))
x = (a=2, b=4, c=1.0, d="test");
x[4] == x.dDictionaries
Similarly to Python, Julia has dictionaries: associative collections of key/value pairs:
Dict("a"=>1, "b"=>2, "c"=>3)Arrays
Arrays are mutable, indexable, homogeneous collections of elements.
One dimension
Unidimensional arrays of one element:
[3]
[3.4]
["Hello, World!"]Unidimensional arrays of multiple elements:
[3, 4]Arrays are homogeneous collections, but look how Julia's abstract types make the following array possible:
[3, "hello"]These 4 syntaxes are equivalent:
[2
4
8]
[2; 4; 8]
vcat(2, 4, 8)
cat(2, 4, 8, dims=1)Two dimensions
[3 4]
[[1, 3] [1, 2]]These 3 syntaxes are equivalent:
[2 4 8]
hcat(2, 4, 8)
cat(2, 4, 8, dims=2)Syntax subtleties
Elements separated by semi-colons or end of line get expanded vertically. Those separated by commas do not get expanded. Elements separated by spaces or tabs get expanded horizontally.
[1:2; 3:4]
[1:2
3:4]
[1:2, 3:4]
[1:2 3:4]Initializing arrays
Here are a few of the functions initializing arrays:
rand(2, 3, 4)
rand(Int64, 2, 3, 4)
zeros(Int64, 2, 5)
ones(2, 5)
reshape([1, 2, 4, 2], (2, 2))
fill("test", (2, 2))Comprehensions
Julia has comprehensions similar to Python:
[ 3i + j for i=1:10, j=3 ]Indexing
As in other mathematically oriented languages such as R, Julia starts indexing at 1.
Indexing is done with square brackets:
a = [1 2; 3 4]
a[1, 1]
a[1, :]
a[:, 1]
b = ["wrong" "wrong" "wrong"; "wrong" "wrong" "wrong"; "wrong" "you got it" "wrong"]As in Python, by default, arrays are passed by sharing:
a = [1, 2, 3];
a[1] = 0;
aThis prevents the unwanted copying of arrays.