## digitalmars.D.learn - Subarrays of arrays

• Omid (10/10) Dec 30 2012 Hi, I am new to D and would like to know if there is any built in
• bearophile (14/20) Dec 30 2012 This gives a range, not an array, so if you want an array, you
• Omid (3/25) Dec 30 2012 Thanks, though I didn't understand a word you said:). I should
• bearophile (21/22) Dec 30 2012 This code works with the latest beta compiler:
• Omid (4/25) Dec 31 2012 Thanks again. I started learning std.array and I should say it
• Omid (2/3) Dec 31 2012 Actually, std.array and std.range both.
"Omid" <mehdioa gmail.com> writes:
Hi, I am new to D and would like to know if there is any built in
feature for accessing a subarray (uni or multi dimensional) of an
array. For example let

arr = [[1,2,3,4,5,6],[7,8,9,10,11,12],[13,14,15,16,17,18]]

I want to obtain a subarray like

assert(arr[][0] == [1,7,13]);
assert(arr[1][] == [7,8,9,10,11,12];
assert(arr[0,2][1] == [2,14]);
assert(arr[0,2][0..3,5] == [[1,2,3,6],[13,14,15,18]]);

Thank you.
Dec 30 2012
"bearophile" <bearophileHUGS lycos.com> writes:
Omid:

arr = [[1,2,3,4,5,6],[7,8,9,10,11,12],[13,14,15,16,17,18]]

I want to obtain a subarray like

assert(arr[][0] == [1,7,13]);
This gives a range, not an array, so if you want an array, you have to call std.array.array later: http://dlang.org/phobos/std_range.html#transversal
assert(arr[1][] == [7,8,9,10,11,12];
Just use array[1]. Or array[1].dup is you want a copy.
assert(arr[0,2][1] == [2,14]);
Enumerated indexes are not supported, so you need a iota + filter + transversal + array.
assert(arr[0,2][0..3,5] == [[1,2,3,6],[13,14,15,18]]);
This requires a iota + filter + chain + array, or something like that. If you don't want to do all this, you have to write your slicing and dicing array struct :-( Someday it will probably be present in Phobos. Bye, bearophile
Dec 30 2012
"Omid" <mehdioa gmail.com> writes:
On Sunday, 30 December 2012 at 12:51:58 UTC, bearophile wrote:
Omid:

arr = [[1,2,3,4,5,6],[7,8,9,10,11,12],[13,14,15,16,17,18]]

I want to obtain a subarray like

assert(arr[][0] == [1,7,13]);
This gives a range, not an array, so if you want an array, you have to call std.array.array later: http://dlang.org/phobos/std_range.html#transversal
assert(arr[1][] == [7,8,9,10,11,12];
Just use array[1]. Or array[1].dup is you want a copy.
assert(arr[0,2][1] == [2,14]);
Enumerated indexes are not supported, so you need a iota + filter + transversal + array.
assert(arr[0,2][0..3,5] == [[1,2,3,6],[13,14,15,18]]);
This requires a iota + filter + chain + array, or something like that. If you don't want to do all this, you have to write your slicing and dicing array struct :-( Someday it will probably be present in Phobos. Bye, bearophile
Thanks, though I didn't understand a word you said:). I should learn iota, filter, transversal first.
Dec 30 2012
"bearophile" <bearophileHUGS lycos.com> writes:
Omid:

Thanks, though I didn't understand a word you said:).
This code works with the latest beta compiler: import std.algorithm: filter, equal, map, canFind; import std.range: transversal, iota; void main() { auto arr = [[ 1, 2, 3, 4, 5, 6], [ 7, 8, 9,10,11,12], [13,14,15,16,17,18]]; auto r1 = transversal(arr, 0); assert(r1.equal([1, 7, 13])); assert(arr[1] == [7,8,9,10,11,12]); auto r2 = [0, 2] .map!(i => arr[i])() .transversal(1); assert(r2.equal([2, 14])); auto r3 = [0, 2] .map!(i => arr[i][0..3] ~ arr[i][5])(); assert(r3.equal([[1,2,3,6],[13,14,15,18]])); } Bye, bearophile
Dec 30 2012
"Omid" <mehdioa gmail.com> writes:
On Sunday, 30 December 2012 at 18:55:50 UTC, bearophile wrote:
Omid:

This code works with the latest beta compiler:

import std.algorithm: filter, equal, map, canFind;
import std.range: transversal, iota;

void main() {
auto arr = [[ 1, 2, 3, 4, 5, 6],
[ 7, 8, 9,10,11,12],
[13,14,15,16,17,18]];

auto r1 = transversal(arr, 0);
assert(r1.equal([1, 7, 13]));

assert(arr[1] == [7,8,9,10,11,12]);

auto r2 = [0, 2]
.map!(i => arr[i])()
.transversal(1);
assert(r2.equal([2, 14]));

auto r3 = [0, 2]
.map!(i => arr[i][0..3] ~ arr[i][5])();
assert(r3.equal([[1,2,3,6],[13,14,15,18]]));
}

Bye,
bearophile
Thanks again. I started learning std.array and I should say it fits all my needs as a mathematics and combinatorics researcher. Now I think I am able to give up commercial softwares.
Dec 31 2012
"Omid" <mehdioa gmail.com> writes:
On Monday, 31 December 2012 at 13:29:02 UTC, Omid wrote:

I started learning std.array
Actually, std.array and std.range both.
Dec 31 2012