www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Is there a way to map associative arrays

reply "Freddy" <Hexagonalstar64 gmail.com> writes:

import std.algorithm;
import std.stdio;
uint[uint] test;

void main(){
	test=[0:2 ,1:3 ,2:4];
	writeln(test.map!(a=>a-2));
}

$ ./test.d
./test.d(8): Error: template std.algorithm.map cannot deduce
function from argument types !((a) => a - 2)(uint[uint]),
candidates are:
/usr/include/dmd/phobos/std/algorithm.d(375):
std.algorithm.map(fun...) if (fun.length >= 1)
Failed: ["dmd", "-v", "-o-", "./test.d", "-I."]
Aug 01 2014
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Freddy:


 uint[uint] test;

 void main(){
 	test=[0:2 ,1:3 ,2:4];
 	writeln(test.map!(a=>a-2));
 }


If you need keys or values you have .keys .values, .byKey, 
.byValue (the first two are eager). If you need both you are out 
of luck, and if you want to write safe code it's better to use a 
foreach loop. If you want to live dangerously you can use a 
test.byKey.zip(test.byValue).

Take a look in Rosettacode, there are examples for all of them.

Bye,
bearophile
Aug 01 2014
parent reply "Freddy" <Hexagonalstar64 gmail.com> writes:
On Friday, 1 August 2014 at 23:22:06 UTC, bearophile wrote:

 Freddy:


 uint[uint] test;

 void main(){
 	test=[0:2 ,1:3 ,2:4];
 	writeln(test.map!(a=>a-2));
 }


 If you need keys or values you have .keys .values, .byKey, 
 .byValue (the first two are eager). If you need both you are 
 out of luck, and if you want to write safe code it's better to 
 use a foreach loop. If you want to live dangerously you can use 
 a test.byKey.zip(test.byValue).

 Take a look in Rosettacode, there are examples for all of them.

 Bye,
 bearophile


Sorry, i wasn't very clear.
I wanted to know if there a way to lazily change the look up
operation
eg:
assert(test[1]==1);
assert(test[2]==2);
Aug 01 2014
parent "Brian Schott" <briancschott gmail.com> writes:
On Friday, 1 August 2014 at 23:33:22 UTC, Freddy wrote:

 On Friday, 1 August 2014 at 23:22:06 UTC, bearophile wrote:

 Freddy:


 uint[uint] test;

 void main(){
 	test=[0:2 ,1:3 ,2:4];
 	writeln(test.map!(a=>a-2));
 }


 If you need keys or values you have .keys .values, .byKey, 
 .byValue (the first two are eager). If you need both you are 
 out of luck, and if you want to write safe code it's better to 
 use a foreach loop. If you want to live dangerously you can 
 use a test.byKey.zip(test.byValue).

 Take a look in Rosettacode, there are examples for all of them.

 Bye,
 bearophile


 Sorry, i wasn't very clear.
 I wanted to know if there a way to lazily change the look up
 operation
 eg:
 assert(test[1]==1);
 assert(test[2]==2);


Give your struct/class a method called "opIndex".

http://dlang.org/operatoroverloading.html#Array
Aug 01 2014