Associative array/Merging

Associative array/Merging is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Task

Define two associative arrays, where one represents the following "base" data:

Key	Value
"name"	"Rocket Skates"
"price"	12.75
"color"	"yellow"

And the other represents "update" data:

Key	Value
"price"	15.25
"color"	"red"
"year"	1974

Merge these into a new associative array that contains every key found in either of the source ones. Each key should map to the value in the second (update) table if that exists, or else to the value in the first (base) table. If possible, do this in a way that does not mutate the original two associative arrays. Obviously this should be done in a way that would work for any data, not just the specific data given here, but in this example the result should be:

Key	Value
"name"	"Rocket Skates"
"price"	15.25
"color"	"red"
"year"	1974

Factor

The assoc-union word does this. assoc-union! is a variant that mutates the first associative array.

Works with: Factor version 0.99 2019-10-06

<lang factor>USING: assocs prettyprint ;

{ { "name" "Rocket Skates" } { "price" 12.75 } { "color" "yellow" } } { { "price" 15.25 } { "color" "red" } { "year" 1974 } } assoc-union .</lang>

Output:

V{
    { "name" "Rocket Skates" }
    { "price" 15.25 }
    { "color" "red" }
    { "year" 1974 }
}

Go

<lang go>package main

import "fmt"

type assoc map[string]interface{}

func merge(base, update assoc) assoc {

   result := make(assoc)
   for k, v := range base {
       result[k] = v
   }
   for k, v := range update {
       result[k] = v
   }
   return result

}

func main() {

   base := assoc{"name": "Rocket Skates", "price": 12.75, "color": "yellow"}
   update := assoc{"price": 15.25, "color": "red", "year": 1974}
   result := merge(base, update)
   fmt.Println(result)

}</lang>

Output:

map[color:red name:Rocket Skates price:15.25 year:1974]

JavaScript

<lang javascript>(() => {

   'use strict';

   console.log(JSON.stringify(
       Object.assign({}, // Fresh dictionary.
           { // Base.
               "name": "Rocket Skates",
               "price": 12.75,
               "color": "yellow"
           }, { // Update.
               "price": 15.25,
               "color": "red",
               "year": 1974
           }
       ), 
       null, 2
   ))

})();</lang>

Output:

{
  "name": "Rocket Skates",
  "price": 15.25,
  "color": "red",
  "year": 1974
}

Lua

<lang Lua>base = {name="Rocket Skates", price=12.75, color="yellow"} update = {price=15.25, color="red", year=1974}

--clone the base data -- result = {} for key,val in pairs(base) do

   result[key] = val

end

--copy in the update data -- for key,val in pairs(update) do

   result[key] = val

end

--print the result -- for key,val in pairs(result) do

   print(string.format("%s: %s", key, val))

end</lang>

Output:

price: 15.25
color: red
year: 1974
name: Rocket Skates

MiniScript

MiniScript supports merging maps with the + operator. <lang MiniScript>base = {"name":"Rocket Skates", "price":12.75, "color":"yellow"} update = {"price":15.25, "color":"red", "year":1974}

result = base + update

print result</lang>

Output:

{"color": "red", "name": "Rocket Skates", "price": 15.25, "year": 1974}

Perl 6

Works with: Rakudo version 2019.11

I must say I somewhat disagree with the terminology. The requested operation is an update not a merge. Demonstrate both an update and a merge. Associative arrays are commonly called hashes in Perl 6.

<lang perl6># Show original hashes say my %base = :name('Rocket Skates'), :price<12.75>, :color<yellow>; say my %update = :price<15.25>, :color<red>, :year<1974>;

1. Need to assign to anonymous hash (or a named hash) to get the desired results and avoid mutating

say "\nUpdate:\n", join "\n", %=%base, %update;

say "\nMerge:\n", join "\n", ((%=%base).push: %update)».join: ', ';

1. Demonstrate unmutated hashes

say "\n", %base, "\n", %update;</lang>

Output:

{color => yellow, name => Rocket Skates, price => 12.75}
{color => red, price => 15.25, year => 1974}

Update:
price	15.25
name	Rocket Skates
year	1974
color	red

Merge:
color	yellow, red
year	1974
name	Rocket Skates
price	12.75, 15.25

{color => yellow, name => Rocket Skates, price => 12.75}
{color => red, price => 15.25, year => 1974}

Python

As of Python 3.5, this can be solved with the dictionary unpacking operator. <lang Python>base = {"name":"Rocket Skates", "price":12.75, "color":"yellow"} update = {"price":15.25, "color":"red", "year":1974}

result = {**base, **update}

print(result)</lang>

Output:

{'name': 'Rocket Skates', 'price': 15.25, 'color': 'red', 'year': 1974}

zkl

<lang zkl>base:=Dictionary(

  "name", 	"Rocket Skates",
  "price", 	12.75,
  "color", 	"yellow",);

update:=Dictionary(

  "price", 	15.25,
  "color", 	"red",
  "year", 	1974,);

update.pump( new:=base.copy() );

new.pump(Void,fcn([(k,v)]){ println("%s\t%s".fmt(k,v)) });</lang>

Output:

price	15.25
color	red
year	1974
name	Rocket Skates