Update value of a key in nested map/list

Questions / Help
1

I’m a bit stuck.

%{"TopKey" => [
	%{"StringKey" => "foo"},
	%{"StringKey" => "bar"}
	]
}

I have a map, containing a list of maps, as above.

I’m struggling to find the correct combination of list/map operations to perform an in-situ string operation on the value of ‘StringKey’.

Most examples of manipulation of nested structures deal solely with maps or lists, not combinations thereof.

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2 
my_data = %{"TopKey" => [
               %{"StringKey" => "foo"},
               %{"StringKey" => "bar"}
             ]
           }
all = fn :get_and_update, data, next ->
  Enum.map(data, next) |> :lists.unzip
end
IO.inspect get_and_update_in(my_data, ["TopKey", all, "StringKey"], &{&1, String.upcase &1})

{["foo", "bar"], %{"TopKey" => [%{"StringKey" => "FOO"}, %{"StringKey" => "BAR"}]}}

From Kernel.get_and_update_in/3

my_data = %{"TopKey" => [
               %{"StringKey" => "foo"},
               %{"StringKey" => "bar"}
             ]
           }
IO.inspect (update_in my_data, ["TopKey", Access.all(), "StringKey"], &String.upcase/1)

%{"TopKey" => [%{"StringKey" => "FOO"}, %{"StringKey" => "BAR"}]}

From Access behaviour

7 Likes
3

Thank you!
I’d found Kernel.update_in, but the Access.all() was what I was missing.

Cheers!

1 Like