📂Julia

Referencing Specific Positions in an Array with Functions in Julia

Overview

When multiple arrays are given, there are often situations where one wants to access a specific element of these arrays, for example, the third element in each array. In Julia, this can be implemented through broadcasting the getindex() function.

Code

getindex.()

julia> seq_ = [collect(1:k:100) for k in 1:10]
10-element Vector{Vector{Int64}}:
 [1, 2, 3, 4, 5, 6, 7, 8, 9, 10  …  91, 92, 93, 94, 95, 96, 97, 98, 99, 100]
 [1, 3, 5, 7, 9, 11, 13, 15, 17, 19  …  81, 83, 85, 87, 89, 91, 93, 95, 97, 99]
 [1, 4, 7, 10, 13, 16, 19, 22, 25, 28  …  73, 76, 79, 82, 85, 88, 91, 94, 97, 100]
 [1, 5, 9, 13, 17, 21, 25, 29, 33, 37  …  61, 65, 69, 73, 77, 81, 85, 89, 93, 97]
 [1, 6, 11, 16, 21, 26, 31, 36, 41, 46, 51, 56, 61, 66, 71, 76, 81, 86, 91, 96]
 [1, 7, 13, 19, 25, 31, 37, 43, 49, 55, 61, 67, 73, 79, 85, 91, 97]
 [1, 8, 15, 22, 29, 36, 43, 50, 57, 64, 71, 78, 85, 92, 99]
 [1, 9, 17, 25, 33, 41, 49, 57, 65, 73, 81, 89, 97]
 [1, 10, 19, 28, 37, 46, 55, 64, 73, 82, 91, 100]
 [1, 11, 21, 31, 41, 51, 61, 71, 81, 91]

julia> getindex.(seq_, 3)
10-element Vector{Int64}:
  3
  5
  7
  9
 11
 13
 15
 17
 19
 21

first(), last()

first() is the same as getindex(, 1), but last() is special because there is no equivalent expression like getindex(, end). It’s often necessary to get the last result as the program iterates, and the index of that last element can vary greatly, so it’s good to know the last() function.

julia> first.(seq_)
10-element Vector{Int64}:
 1
 1
 1
 1
 1
 1
 1
 1
 1
 1

julia> last.(seq_)
10-element Vector{Int64}:
 100
  99
 100
  97
  96
  97
  99
  97
 100
  91

Environment

• OS: Windows
• julia: v1.9.0