Associative array/Creation: Difference between revisions
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Numerous methods exist for the mapping type http://docs.python.org/lib/typesmapping.html |
Numerous methods exist for the mapping type http://docs.python.org/lib/typesmapping.html |
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==[[Ruby]]== |
==[[Ruby]]== |
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@hash->{'key1', 'three'} = ('val1', -238.83); |
@hash->{'key1', 'three'} = ('val1', -238.83); |
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==[[Python]]== |
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[[Category:Python]] |
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In Python, hashes are called dictionaries. |
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==[[Smalltalk]]== |
==[[Smalltalk]]== |
Revision as of 16:36, 8 February 2007
You are encouraged to solve this task according to the task description, using any language you may know.
In this task, the goal is to create an associative array.
C++
Compiler: g++ 4.0.2
#include <map> #include <string> #include <iostream> #include <ostream> int main() { // This is an associative array which maps strings to ints typedef std::map<std::string, int> colormap_t; colormap_t colormap; // First, populate it with some values colormap["red"] = 0xff0000; colormap["green"] = 0x00ff00; colormap["blue"] = 0x0000ff; colormap["my favourite color"] = 0x00ffff; // then, get some values out int color = colormap["green"]; // color gets 0x00ff00 color = colormap["black"]; // accessing unassigned values assigns them to 0 // get some value out without accidentally inserting new ones colormap_t::iterator i = colormap.find("green"); if (i == colormap.end()) { std::cerr << "color not found!\n"; } else { color = i->second; } // Now I changed my mind about my favourite color, so change it colormap["my favourite color"] = 0x337733; // print out all defined colors for (colormap_t::iterator i = colormap.begin(); i != colormap.end(); ++i) std::cerr << "colormap[\"" << i->first << "\"] = 0x" << std::hex << i->second << "\n"; }
A simpler example which only creates the array and assigns a value.
Compiler: g++ 4.0.2
#include <map> #include <string> int main( int argc, char* argv[] ) { std::map< std::string, std::string > hash ; hash[ "key-1" ] = "val1" ; }
C#
Platform: .NET 1.x
System.Collections.HashTable map = new System.Collections.HashTable(); map["key1"] = "foo";
Platform: .NET 2.0
Dictionary<string, string> map = new Dictionary<string,string>(); map[ "key1" ] = "foo";
ColdFusion
<cfset myHash = structNew()> <cfset myHash.key1 = "foo"> <cfset myHash["key2"] = "bar"> <cfset myHash.put("key3","java-style")>
In ColdFusion, a map is literally a java.util.HashMap, thus the above 3rd method is possible.
Common Lisp
;; default :test is #'eql, which is suitable for numbers only, ;; or for implementation identity for other types! ;; Use #'equalp if you want case-insensitive keying on strings.
(setf my-hash (make-hash-table :test #'equal)) (setf (gethash "H2O" my-hash) "Water") (setf (gethash "HCl" my-hash) "Hydrochloric Acid") (setf (gethash "CO" my-hash) "Carbon Monoxide")
D
int[char[]] hash; hash["foo"] = 42; hash["bar"] = 100; assert("foo" in hash);
Haskell
Interpreter: GHCi
import Data.Map dict = fromList [("key1","val1"), ("key2","val2")]
Java
Defining a Map
Map<String, Integer> map = new HashMap<String, Integer>(); map.put("foo", 5); map.put("bar", 10); map.put("baz", 15);
Retreiving a value
map.get("foo") // => 5 map.get("invalid") // => null
Iterate over keys
for (String key: map.keySet()) System.out.println(key);
Iterate over values
for (int value: map.values()) System.out.println(value);
Iterate over key,values
for (Map.Entry<String, Integer> entry: map.entrySet()) System.out.println(entry.getKey() + " => " + entry.getValue());
JavaScript
In Javascript we make an associative array from an empty object, otherwise if we make it from an array we'll get all the Array object's method and properties when we iterate over it
var assoc = {}; assoc['foo'] = 'bar'; assoc['another-key'] = 3; assoc.thirdKey = 'we can also do this!'; for(key in assoc) { alert('key:"'+key+'", value:"'+assoc[key]+'"'); }
The above associative array can also be constructed using Javascript's object literal syntax
var assoc = { foo:'bar', 'another-key':3, //the key can either be enclosed by quotes or not thirdKey = 'we can also do this!' };
Lua
Lua tables are Hashes
hash = {} hash[ "key-1" ] = "val1" hash[ "key-2" ] = 1 hash[ "key-3" ] = {}
Returns nil on unknown key.
Objective-C
Compiler: gcc
In Objective C, you will use the NSMutableDictionary class to create a hash. To map to an integer, you will also need to make use of the NSNumber class.
NSMutableDictionary *dict = [[NSMutableDictionary alloc] init]; [dict setObject:[NSNumber numberWithInt:2] forKey:@"Two"]; [dict setObject:[NSNumber numberWithInt:7] forKey:@"Seven"]; int two = [[dict objectForKey:@"Two"] intValue]; int seven = [[dict objectForKey:@"Seven"] intValue]; NSLog( @"%d, %d", two, seven );
OCaml
A simple idiom to create a hash table mapping strings to integers:
let hash = Hashtbl.create 0;; List.iter (fun (key, value) -> Hashtbl.add hash key value) ["foo", 5; "bar", 10; "baz", 15];;
To retrieve a value:
let bar = Hashtbl.find hash "bar";; (* bar = 5 *)
To retrieve a value, returning a default if the key is not found:
let quux = try Hashtbl.find hash "quux" with Not_found -> some_value;;
PHP
$array = array(); $array['foo'] = 'bar'; $array['bar'] = 'foo'; echo($array['foo']); // bar echo($array['moo']); // Undefined index
//alternative (inline) way $array2 = array('fruit'=>'apple, 'price'=>12.96, 'colour'=>'green');
Python
Hashes are a built-in type called dictionaries (or mappings) in Python.
hash = dict() # 'dict' is the dictionary type. hash = dict(red="FF0000", green="00FF00", blue="0000FF") hash = { 'key1':1, 'key2':2, } value = hash[key]
Numerous methods exist for the mapping type http://docs.python.org/lib/typesmapping.html
# empty dictionary d = {} d['spam'] = 1 d['eggs'] = 2
# dictionaries with two keys d1 = {'spam': 1, 'eggs': 2} d2 = dict(spam=1, eggs=2)
# dictionaries from tuple list d1 = dict([('spam', 1), ('eggs', 2)]) d2 = dict(zip(['spam', 'eggs'], [1, 2]))
# iterating over keys for key in d: print key, d[key]
# iterating over (key, value) pairs for key, value in d.iteritems(): print key, value
Create a generic mapping function that applys a callback to elements in a list:
Ruby
A hash object that returns nil for unknown keys
hash={} hash[666]='devil' hash[777] # => nil hash[666] # => 'devil'
A hash object that returns 'unknown key' for unknown keys
hash=Hash.new('unknown key') hash[666]='devil' hash[777] # => 'unknown key' hash[666] # => 'devil'
A hash object that returns "unknown key #{key}" for unknown keys
hash=Hash.new{|h,k|h[k]="unknown key #{k}"} hash[666]='devil' hash[777] # => 'unknown key 777' hash[666] # => 'devil'
Iterate over key/value
foreach($array as $key => $value) { echo('Key: '.$key.' Value: '.$value); }
Scala
// immutable maps var map = Map(1 -> 2, 3 -> 4, 5 -> 6) map(3) // 4 map = map + (44 -> 99) // maps are immutable, so we have to assign the result of adding elements map.isDefinedAt(33) // false map.isDefinedAt(44) // true
// mutable maps (HashSets) import scala.collection.mutable.HashMap val hash = new HashMap[int, int] hash + (1 -> 2) hash + (3 -> 4, 5 -> 6, 44 -> 99) hash(44) // 99 hash.isDefinedAt(33) // false hash.isDefinedAt(44) // true
// iterate over key/value hash.foreach {k => Console.println("key "+k._1+" value "+k._2)} // k is a 2 element Tuple
// remove items where the key is <= 3 map.filter {k => k._1 > 3} // Map(5 -> 6, 44 -> 99)
Perl
Interpeter: Perl
Defining a Hash
# using => key does not need to be quoted unless it contains special chars my %hash = ( key1 => 'val1', 'key-2' => 2, three => -238.83, 4 => 'val3', ); # using , both key and value need to be quoted if containing something non-numeric in nature my %hash = ( 'key1', 'val1', 'key-2', 2, 'three', -238.83, 4, 'val3', );
Defining a HashRef
my $hashref = { key1 => 'val1', 'key-2' => 2, three => -238.83, 4 => 'val3', }
Using a Hash
print $hash{'key1'}; $hash{'key1'} = 'val1'; @hash{'key1', 'three'} = ('val1', -238.83);
Using a HashRef
print $hash->{'key1'}; $hash->{'key1'} = 'val1'; @hash->{'key1', 'three'} = ('val1', -238.83);
Smalltalk
"Tested with Dolphin Smalltalk" states := Dictionary new. states at: 'MI' put: 'Michigan'. states at: 'MN' put: 'Minnesota'.
Tcl
All arrays in Tcl are associative.
# Create one element at a time: set hash(foo) 5
# Create in bulk: array set hash { foo 5 bar 10 baz 15 }
# Access one element: set value $hash(foo)
# Output all values: foreach key [array names hash] { puts $hash($key) }