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Idiom #335 List to map

Create the map m containing all the elements e of the list a, using as key the field e.id.

import java.util.HashMap;
import java.util.Map;
Map<Integer, E> m = new HashMap<>() {{
    for (var x : a) put(x.id, x);
}};
import java.util.HashMap;
import java.util.List;
import java.util.Map;
class IdMap extends HashMap<Integer, E> {
    IdMap(List<E> x) { putAll(x); }
    E put(E x) {
        return super.put(x.id, x);
    }
    void putAll(List<E> x) {
        x.forEach(this::put);
    }
}
Map<Integer, E> m = new IdMap(a);
import java.util.HashMap;
import java.util.Map;
Map<Integer, E> m = new HashMap<>();
for (var x : a) m.put(x.id, x);
import java.util.Map;
Map<?, E> m = a.stream()
    .collect(toMap(x -> x.id, x -> x));
var m = a.ToDictionary(e => e.id, e => e);
final m = {
  for (final e in a) e.id: e,
};
m := make(map[K]V, len(a))
for _, e := range a {
	m[e.id] = e
}
let m = new Map(a.map(e => [e.id, e]))
local m={}
for _,e in ipairs(a) do
 m[e.id]=e
end
fgl
type
  TList = specialize TFPGList<TData>;
  TMap = specialize TFPGMap<TKey, TData>;

var
  a: TList;
  m: TMap;
  idx: integer;

begin
  ....
  m := TMap.Create;
  for idx := 0 to a.count-1 do
  begin
    m.add(a.items[idx].e, a.items[idx]);
  end;
  ....
  m.Free;
  ....
foreach my $e (@a) {
    $m{$e->id) = $e;
}
m = dict((x.id, x) for x in a)
m = {e.id:e for e in a}
class AttributeMap(dict):
    def __init__(self, attribute, *args):
        array = []
        for e in args:
            key = getattr(e, attribute)
            array.append((key, e))
        super().__init__(array)
m = AttributeMap('id', *a)
m = a.group_by(&:id)
use std::collections::HashMap;
let mut m = HashMap::new();

for e in a {
	m.entry(e.id).or_insert_with(Vec::new).push(e);
}
New implementation...
< > ⌨
programming-idioms.org 
Map<Integer, E> m = new HashMap<>() {{
    for (var x : a) put(x.id, x);
}};
class IdMap extends HashMap<Integer, E> {
    IdMap(List<E> x) { putAll(x); }
    E put(E x) {
        return super.put(x.id, x);
    }
    void putAll(List<E> x) {
        x.forEach(this::put);
    }
}
Map<Integer, E> m = new IdMap(a);
Map<Integer, E> m = new HashMap<>();
for (var x : a) m.put(x.id, x);
Map<?, E> m = a.stream()
    .collect(toMap(x -> x.id, x -> x));
var m = a.ToDictionary(e => e.id, e => e);
final m = {
  for (final e in a) e.id: e,
};
m := make(map[K]V, len(a))
for _, e := range a {
	m[e.id] = e
}
let m = new Map(a.map(e => [e.id, e]))
local m={}
for _,e in ipairs(a) do
 m[e.id]=e
end
type
  TList = specialize TFPGList<TData>;
  TMap = specialize TFPGMap<TKey, TData>;

var
  a: TList;
  m: TMap;
  idx: integer;

begin
  ....
  m := TMap.Create;
  for idx := 0 to a.count-1 do
  begin
    m.add(a.items[idx].e, a.items[idx]);
  end;
  ....
  m.Free;
  ....
foreach my $e (@a) {
    $m{$e->id) = $e;
}
m = dict((x.id, x) for x in a)
m = {e.id:e for e in a}
class AttributeMap(dict):
    def __init__(self, attribute, *args):
        array = []
        for e in args:
            key = getattr(e, attribute)
            array.append((key, e))
        super().__init__(array)
m = AttributeMap('id', *a)
m = a.group_by(&:id)
let mut m = HashMap::new();

for e in a {
	m.entry(e.id).or_insert_with(Vec::new).push(e);
}