Hash from two arrays

Using two Arrays of equal length, create a Hash object where the elements from one array (the keys) are linked to the elements of the other (the values)

By strict definition a std::map is not a hash, but it provides the same functionality. The C++-200x update to the C++ standard is incorporating hashes. When they are standardized the code below can change std::map to std::unordered_map and this will technically be a hash table. The core idea, turning two sequences into an associative mapping, is valid either way.

<lang cpp> #include <map>

#include <string>

int
main( int argc, char* argv[] )
{
 std::string keys[] = { "1", "2", "3" } ;
 std::string vals[] = { "a", "b", "c" } ;
 
 std::map< std::string, std::string > hash ;
 
 for( int i = 0 ; i < 3 ; i++ )
 {
  hash[ keys[i] ] = vals[i] ;
 }
}</lang>

Alternatively: <lang cpp> #include <map> // for std::map

#include <algorithm> // for std::transform
#include <string>    // for std::string
#include <utility>   // for std::make_pair

int main()
{
  std::string keys[] = { "one", "two", "three" };
  std::string vals[] = { "foo", "bar", "baz" };

  std::map<std::string, std::string> hash;

  std::transform(keys, keys+3,
                 vals,
                 std::inserter(hash, hash.end()),
                 std::make_pair<std::string, std::string>);
}</lang>

C#

<lang csharp> System.Collections.HashTable h = new System.Collections.HashTable();

 string[] arg_keys = {"foo","bar","val"};
 string[] arg_values = {"little", "miss", "muffet"};
   
 //Some basic error checking
 int arg_length = 0;
 if ( arg_keys.Length == arg_values.Length ) {
   arg_length = arg_keys.Length;
 }
 
 for( int i = 0; i < arg_length; i++ ){
   h.add( arg_keys[i], arg_values[i] ); 
 }</lang>

Alternate way of adding values

<lang csharp> for( int i = 0; i < arg_length; i++ ){

   h[ arg_keys[i] ] = arg_values[i]; 
 }</lang>

D

<lang d> string[] keys = ["one", "two", "three"]

int[] values  = [1, 2, 3];

int[string] hash;

foreach(idx, key; keys)
  hash[key] = values[idx];</lang>

E

def keys := ["one", "two", "three"]
def values := [1, 2, 3]
__makeMap.fromColumns(keys, values)

Factor

USING: hashtables ;
{ "one" "two" "three" } { 1 2 3 } zip >hashtable

Groovy

<lang groovy> keys = ['a','b','c']

vals = ['aaa', 'bbb', 'ccc']
hash = [:]
i = 0
keys.each { entry ->
 hash.put(entry, vals[i++]) 
}</lang>

Haskell

Works with: GHCi version 6.6

<lang haskell> import Data.Map

makeMap ks vs = fromList $ zip ks vs
mymap = makeMap ['a','b','c'] [1,2,3]</lang>

J

f=: y {~ x&i.

For example:

   x=: 10?.100 
   y=: > ;:'zero one two three four five six seven eight nine'
   f=: y {~ x&i.

   x
46 99 23 62 42 44 12 5 68 63
   $y
10 5

   f 46
zero 
   f 99
one  
   f 63 5 12 5 23
nine 
seven
six  
seven
two

Here, x is a list of 10 integers between 0 and 99 chosen at random without repetition, and y is a 10 by 5 character matrix.

Java

import java.util.HashMap;
public static void main(String[] args){
	String[] keys= {"a", "b", "c"};
	int[] vals= {1, 2, 3};
	HashMap<String, Integer> hash= new HashMap<String, Integer>();

	for(int i= 0; i < keys.length; i++){
	   hash.put(keys[i], vals[i]);
	}
}

JavaScript

var keys = ['a', 'b', 'c'];
var values = [1, 2, 3];
var map = {};
for(var i in keys) {
  map[ keys[i] ] = values[i];
}

Objective-C

NSArray *keys = [NSArray arrayWithObjects:@"a", @"b", @"c", nil];
NSArray *values = [NSArray arrayWithObjects:[NSNumber numberWithInt:1],
                                            [NSNumber numberWithInt:2],
                                            [NSNumber numberWithInt:3], nil];
NSDictionary *dict = [NSDictionary dictionaryWithObjects:values forKeys:keys];

OCaml

The idiomatic solution uses lists rather than arrays.

 let keys = [ "foo"; "bar"; "baz" ]
 and vals = [ 16384; 32768; 65536 ]
 and hash = Hashtbl.create 0;;

 List.iter2 (Hashtbl.add hash) keys vals;;

In the extremely unlikely event that it was actually necessary to use arrays, the solution would become slightly less elegant: (except using the ExtLib which provides the equivalent Array.iter2)

 let keys = [| "foo"; "bar"; "baz" |]
 and vals = [| 16384; 32768; 65536 |]
 and hash = Hashtbl.create 0;;

 for i = 0 to Array.length keys - 1 do
   Hashtbl.add hash keys.(i) vals.(i)
 done;;

In either case, an exception is raised if the inputs are different lengths.

Perl

Works with: Perl version 5

Library: List::MoreUtils MoreUtils

use List::MoreUtils qw(zip);

my @keys = qw(a b c);
my @vals = (1, 2, 3);
my %hash = zip @keys, @vals;

Using no modules:

my %hash;
@hash{qw(a b c)} = (1, 2, 3);

PHP

Works with: PHP version 5

$keys = array('a', 'b', 'c');
$values = array(1, 2, 3);
$hash = array_combine($keys, $values);

Works with: PHP version 4

$keys = array('a', 'b', 'c');
$values = array(1, 2, 3);
$hash = array();
for ($idx = 0; $idx < count($keys); $idx++) {
  $hash[$keys[$idx]] = $values[$idx];
}

Pop11

vars keys = { 1 a b c};
vars vals = { 2 3 valb valc};
vars i;
;;; Create hash table
vars ht = newmapping([], 500, 0, true);
;;; Loop over input arrays (vectors)
for i from 1 to length(keys) do
  vals(i) -> ht(keys(i));
endfor;

Prolog

% this one with side effect hash table creation

:-dynamic hash/2.

make_hash([],[]).
make_hash([H|Q],[H1|Q1]):-
	assert(hash(H,H1)),
	make_hash(Q,Q1).

:-make_hash([un,deux,trois],[[a,b,c],[d,e,f],[g,h,i]])


% this one without side effects 

make_hash_pure([],[],[]).
make_hash_pure([H|Q],[H1|Q1],[hash(H,H1)|R]):-
	make_hash_pure(Q,Q1,R).

:-make_hash_pure([un,deux,trois],[[a,b,c],[d,e,f],[g,h,i]],L),findall(M,(member(M,L),assert(M)),L).

Python

Works with: Python version 2.3+

<lang python> keys = ['a', 'b', 'c'] values = [1, 2, 3] hash = dict(zip(keys, values))

Lazily:

from itertools import izip hash = dict(izip(keys, values)) </lang>

Works with: Python version 3.0+

Shows off the dict comprehensions in Python 3: <lang python> keys = ['a', 'b', 'c'] values = [1, 2, 3] hash = {key: value for key, value in zip(keys, values)} </lang>

Works with: Python

(any version)

<lang python>keys = ['a', 'b', 'c'] values = [1, 2, 3] hash = {} for i range(len(keys)):

   hash[keys[i]] = values[i]

</lang> The original (Ruby) example uses a range of different types as keys. Here is similar in python (run at the shell): <lang python>>>> class Hashable(object): def __hash__(self): return id(self) ^ 0xBEEF

>>> my_inst = Hashable() >>> my_int = 1 >>> my_complex = 0 + 1j >>> my_float = 1.2 >>> my_string = "Spam" >>> my_bool = True >>> my_unicode = u'Ham' >>> my_list = ['a', 7] >>> my_tuple = ( 0.0, 1.4 ) >>> my_set = set(my_list) >>> def my_func(): pass

>>> class my_class(object): pass

>>> keys = [my_inst, my_tuple, my_int, my_complex, my_float, my_string, my_bool, my_unicode, frozenset(my_set), tuple(my_list), my_func, my_class] >>> values = range(12) >>> d = dict(zip(keys, values)) >>> for key, value in d.items(): print key, ":", value

1 : 6 1j : 3 Ham : 7 Spam : 5 (0.0, 1.3999999999999999) : 1 frozenset(['a', 7]) : 8 1.2 : 4 ('a', 7) : 9 <function my_func at 0x0128E7B0> : 10 <class '__main__.my_class'> : 11 <__main__.Hashable object at 0x012AFC50> : 0 >>> </lang>

Raven

[ 'a' 'b' 'c' ] as $keys [ 1 2 3 ] as $vals
$keys $vals combine as $hash

Ruby

 keys=['hal',666,[1,2,3]]
 vals=['ibm','devil',123]
 hash = Hash[*keys.zip(vals).flatten]
 # now hash => {'hal' => 'ibm', 666 => 'devil', [1,2,3] => 123}

 #retrieve the value linked to the key [1,2,3]
 puts hash[ [1,2,3] ]
 #123

Scala

val keys = Array(1, 2, 3)
val values = Array("A", "B", "C")
val map = Map(keys.zip(values) : _*)
// returns Map(1 -> "A", 2 -> "B", 3 -> "C")
// keys.zip(values) is an array of pairs : Array((1, "A"), (2, "B"), (3, "C"))
// Map(...) expects multiple pairs arguments. Syntax ": _*" tells the single argument contains multiple values.

Scheme

Using SRFI 69:

<lang scheme>(define (lists->hash-table keys values . rest)
 (apply alist->hash-table (map cons keys values) rest))</lang>

Seed7

$ include "seed7_05.s7i";

const type: numericHash is hash [string] integer;
var numericHash: myHash is numericHash.value;

const proc: main is func
  local
    var array string: keyList is [] ("one", "two", "three");
    var array integer: valueList is [] (1, 2, 3);
    var integer: number is 0;
  begin
    for number range 1 to length(keyList) do
      myHash @:= [keyList[number]] valueList[number];
    end for;
  end func;

Tcl

Arrays in Tcl are automatically associative, i.e. there are no "not hashed arrays". If we can take "arrays of equal length" to mean "lists of equal length", then the task might look like this: <lang tcl>set keys [list fred bob joe] set values [list barber plumber tailor] array set arr {} foreach a $keys b $values { set arr($a) $b }</lang> Alternatively, a dictionary could be used: <lang tcl>foreach a $keys b $values {

   dict set jobs $a $b

}</lang>

UnixPipes

Using a sorted file as an associative array (see Creating an associative array for usage.)

cat <<VAL >p.values
apple
boy
cow
dog
elephant
VAL

cat <<KEYS >p.keys
a
b
c
d
e
KEYS

paste -d\   <(cat p.values | sort) <(cat p.keys | sort)

Visual Basic .NET

       Dim names = New String() {"Frank", "Tom", "Jones"}
       Dim grades = New Integer() {90, 87, 96}

       Dim hash = New Dictionary(Of String, Integer)
       For i = 0 To names.Length - 1
           hash.Add(names(i), grades(i))
       Next