Get data from a JSON Array - json

Question

I have a JSON array:
response = [
%{
"created_at" => 1542757526,
"email" => "bcs#yahoo.com",
"first_name" => "rana",
"id" => "YW1pcnBheWFyeUB5YWhvby5jb20=",
"last_clicked" => nil,
"last_emailed" => nil,
"last_name" => "amir",
"last_opened" => nil,
"updated_at" => 1542759123
},
%{
"created_at" => 1542757457,
"email" => "abc#gmail.com",
"first_name" => "rana",
"id" => "cmFtaXIyNDI2QGdtYWlsLmNvbQ==",
"last_clicked" => nil,
"last_emailed" => nil,
"last_name" => "amir",
"last_opened" => nil,
"updated_at" => 1542759001
},
# .......
]
I'm trying to get the email field of all items in the response variable. Example:
["bcs#yahoo.com", "xyz#gmail.com", ....]

Answer 1

You're looking for Enum.map/2. This method calls the passed function on every item in the given list/enumerable:
Enum.map(response, fn item -> item["email"] end )
Alternatively, you can use the shorthand and make it concise:
Enum.map(response, &(&1["email"]))
External Resources: See this and also this to understand the concept of mapping in functional programming in general.
Side note: flat_map/2 is a variation of map/2 that expects the "mapped result" to be another list (so it can be joined and flattened with the rest of the mapped results).

Answer 2

In addition to map, you could also look at comprehensions. Essentially they combine the functionality of Enum.map/2 & Enum.filter/2.
They allow you to do something like this:
for %{"email" => email} <- response, do: email
or this:
for item <- response, do: item["email"]
Note there's a subtle difference in behavior between the result of the two: the former will filter out any items that do not match the left-hand side (it will only keep maps with an "email" key), but the latter will map the items lacking an email to nil.