Julia: How To Find Elements in One Array but Not in the Other

Hongtao Hao / 2021-07-14


This post is tested under Julia v1.6.1 and DataFrames v1.2.0.

Base.setdiff will do the trick.

a = [1, 3, 5, 7, 9, 10, 'a', 'e']
b = [2, 4, 9, 11, 7, 'e', 'b']
# To find elements in a but not in b:
setdiff(a, b) # returns [1, 3, 5, 10, 'a']

This works for 2-dimensional arrays as well:

julia> c = [1 2 8; 4 5 6]
2×3 Matrix{Int64}:
 1  2  8
 4  5  6

julia> d = [2 3 4; 8 6 7]
2×3 Matrix{Int64}:
 2  3  4
 8  6  7

julia> setdiff(c, d)
2-element Vector{Int64}:
 1
 5

Note that Base.setdiff!(a,b) will remove in-place from a all elements found in b:

setdiff!(a,b) # returns [1, 3, 5, 10, 'a']
a # returns returns [1, 3, 5, 10, 'a']

References #

Last modified on 2021-07-16