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filter!

filter!(function, collection)

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

Examples

julia> foo = [1:5];

julia> function isOdd(x)
        x % 2 != 0
       end

julia> filter!(isOdd, foo);

julia> foo
3-element Array{Int64,1}:
 1
 3
 5

1. Filter even numbers from an array:

   julia> arr = [1, 2, 3, 4, 5, 6];
   julia> filter!(x -> x % 2 == 0, arr)
   3-element Array{Int64,1}:
   2
   4
   6

   This example filters out the odd numbers from the array arr using the provided function.

2. Filter strings containing specific characters:

   julia> words = ["apple", "banana", "orange", "grape"];
   julia> filter!(x -> contains(x, 'a'), words)
   2-element Array{String,1}:
   "apple"
   "banana"

   It filters the strings from the vector words that contain the character 'a' using the given function.

3. Filter key-value pairs in a dictionary:

   julia> dict = Dict("apple" => 3, "banana" => 2, "orange" => 5, "grape" => 4);
   julia> filter!((k, v) -> v > 3, dict)
   Dict{String,Int64} with 2 entries:
   "orange" => 5
   "grape"  => 4

   This example filters the key-value pairs from the dictionary dict based on the condition that the value is greater than 3.

Common mistake example:

julia> arr = [1, 2, 3, 4, 5];
julia> filter!(x -> x > 5, arr)
ERROR: MethodError: no method matching isless(::Int64, ::Nothing)

In this example, the provided function tries to compare the elements with 5, but there is no comparison defined between Int64 and Nothing. Make sure the function used in filter! is valid for the elements in the collection to avoid such errors.

See Also

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