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@taiansu
Last active January 15, 2019 03:58
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functional practice
students = [
{age: 18, first_name: "Shane", last_name: "Osbourne"},
{age: 22, first_name: "John", last_name: "Doe"},
{age: 12, first_name: "John", last_name: "Barker"},
{age: 40, first_name: "Ben", last_name: "Haskell"},
{age: 34, first_name: "Ben", last_name: "Barker"},
{age: 9, first_name: "Shane", last_name: "Doe"},
{age: 33, first_name: "Lee", last_name: "Ruby"}
]
students
|> Enum.filter(fn s -> s.age > 20 end)
|> Enum.group_by(fn s -> s.first_name end)
|> Enum.map(fn {k, v} ->
last_names = Enum.map(v, fn s -> s.last_name end)
{k, last_names}
end)
|> Enum.into(%{})
|> IO.inspect
let result = R.compose(
R.fromPairs,
R.map(([k, v]) => {
let last_names = R.map(s => s.last_name, v)
return [k, last_names]
}),
R.toPairs,
R.groupBy(s => s.first_name),
R.filter(s => s.age > 20)
)(students);
p result
result =
students.filter { |s| s[:age] > 20}
.group_by { |s| s[:first_name] }
.map do |key, val| # 也可以改用 hash.transform_values
last_names = val.map { |s| s[:last_name] }
[key, last_names]
end
.to_h
p result
students
|> Enum.filter(fn s -> s.age > 20 end)
|> Enum.reduce(%{}, fn %{first_name: first_name, last_name: last_name}, acc ->
prev = acc |> Map.get(first_name) |> List.wrap()
Map.put(acc, first_name, [last_name | prev])
end)
|> IO.inspect()
let result = R.compose(
R.reduce((accu, {first_name, last_name}) => {
let prev = R.propOr([], first_name, accu)
return R.assoc(first_name, [...prev, last_name], accu);
}, {}),
R.filter(s => s.age > 20)
)(students);
console.log(result)
result =
students.filter { |s| s[:age] > 20 }
.reduce({}) do |accu, s|
first_name, last_name = s.values_at(:first_name, :last_name)
prev = Array(accu[first_name])
accu[first_name] = [*prev, last_name]
accu
end
p result
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