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filter

filter(function, collection)

Return a copy of collection, removing elements for which function is false. For associative collections, the function is passed two arguments (key and value).

Examples

julia> filter((x) -> x % 3 == 0, [1:10])        # divisible by 3
3-element Array{Int64,1}:
 3
 6
 9

julia> array = Int[1,2,3]
       filter(x -> x % 2 == 0, array)
1-element Array{Int64,1}:
 2

julia> array = Int[1,2,3]
       filter(x -> x==3, array) 
1-element Array{Int64,1}:
 3

1. Filter elements from an array using a function:

   julia> arr = [1, 2, 3, 4, 5];
   julia> filter(x -> x > 2, arr)
   3-element Array{Int64,1}:
   3
   4
   5

   This example filters out elements from the array arr using the given function x -> x > 2, which keeps only the elements greater than 2.

2. Filter elements from a dictionary based on a condition:

   julia> dict = Dict("apple" => 10, "banana" => 20, "orange" => 15);
   julia> filter((k, v) -> v > 15, dict)
   Dict{String,Int64} with 1 entry:
    "banana" => 20

   Here, the filter function is applied to the dictionary dict using the function (k, v) -> v > 15, which keeps only key-value pairs where the value is greater than 15.

3. Filter strings from an array based on a condition:

   julia> words = ["apple", "banana", "orange", "grape"];
   julia> filter(s -> length(s) > 5, words)
   2-element Array{String,1}:
   "banana"
   "orange"

   This example filters out strings from the array words using the condition length(s) > 5, which keeps only the strings with a length greater than 5.

Common mistake example:

julia> arr = [1, 2, 3, 4, 5];
julia> filter(x -> x < 0, arr)
Int64[]

In this example, the provided filter function x -> x < 0 returns false for all elements in the array arr. As a result, the filtered array becomes empty. It's important to ensure that the filter function returns the desired condition for the elements in the collection to avoid such mistakes.

See Also

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