NestedFilter

The Problems

1. You have a nested map (or a struct that you converted to a nested map) and you want to remove ALL the keys with specific values such as nil.
2. You want to do a Map#take on a nested map

Example: Remove all the map keys with nil values

nested_map = %{a: 1, b: %{c: nil, d: nil}, c: nil}

Map.drop(nested_map, [:c, :d])
# => %{a: 1, b: %{c: nil, d: nil}}

# But you actually wanted:
# => %{a: 1}

The Solution: NestedFilter

NestedFilter drills down into a nested map and can do any of the following:

1. filters out keys according to user specified values.
2. filters out values according to user specified keys.

Installation

If available in Hex, the package can be installed by adding nested_filter to your list of dependencies in mix.exs:

def deps do
  [{:nested_filter, "~> 1.2.2"}]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/nested_filter.

Usage

By default, when removing user specified values, empty values will be preserved (see Case 1 below). You can add empty values to the user specified values list if you wish those "empty values" (e.g., empty maps) to be removed.

NestedFilter.drop_by_value

# Case 1: Remove the nil values from a nested map, preserving empty map values

nested_map = %{a: 1, b: %{m: nil, n: 2}, c: %{p: %{q: nil, r: nil}, s: %{t: 2, u: 3}} }
NestedFilter.drop_by_value(nested_map, [nil])

# => %{a: 1, b: %{n: 2}, c: %{p: %{}, s: %{t: 2, u: 3}} }

# Case 2: Remove the nil values from a nested map, removing empty map values

nested_map = %{a: 1, b: %{m: nil, n: 2}, c: %{p: %{q: nil, r: nil}, s: %{t: 2, u: 3}} }
NestedFilter.drop_by_value(nested_map, [nil, %{}])
# => %{a: 1, b: %{n: 2}, c: %{s: %{t: 2, u: 3}} }

NestedFilter.drop_by_key

# Case 1: Remove values from a nested map by key

nested_map = %{a: 1, b: %{a: 2, b: 3}, c: %{a: %{a: 1, b: 2}, b: 2, c: %{d: 1, e: 2}}}
assert NestedFilter.drop_by_key(nested_map, [:a]) == %{b: %{b: 3},c: %{b: 2, c: %{d: 1, e: 2}}}

NestedFilter.take_by_key

# Case 1: Take values from a nested map by key

nested_map = %{a: %{b: 1}, c: 3, e: %{f: 4}}
assert NestedFilter.take_by_key(nested_map, [:b, :f]) == %{b: 1, f: 4 }

You can browse the tests for more usage examples.