digitalmars.D.learn - Returning multiple arrays from function - struct or byref the only
- Laeeth Isharc (41/41) Oct 15 2014 Hi.
- Laeeth Isharc (18/18) Oct 15 2014 Here is byref:
- Meta (4/45) Oct 15 2014 You could also return an std.typecons.Tuple containing both
- =?UTF-8?B?QWxpIMOHZWhyZWxp?= (13/19) Oct 15 2014 That's my preference. Tuples would work as well but they have two minor
- Laeeth Isharc (3/23) Oct 18 2014 Thanks for the thoughts Meta and Ali.
- Meta (21/24) Oct 18 2014 This works, but I agree it is a bit obscure (you may want to add
- Meta (3/5) Oct 18 2014 "Implicit conversion" is not correct. I meant "implicit
Hi.
I have to write a bunch of functions that operate on input arrays
to return multiple output arrays.
In case helpful the inputs are price bars or economic data points
(datetime, ohlc) and the outputs are nx1 arrays (I won't say
vectors) of doubles or structs.
What is the best way to return multiple arrays in this kind of
situation. In Python I returned a tuple of numpy arrays, and the
C way would be to pass a pointer to the return destinations, and
I guess I could do the same in a D way by passing by ref not
value).
I see that I can return a struct containing dynamic arrays, and
return it (by value of course). I have read the forum discussion
a while back over how to return multiple values, and tried using
tuples. I don't see that I can return a tuple of arrays - am I
missing something?
Here is a simple case. Can I do better ?
Thanks.
import std.typecons;
import std.stdio;
struct RetStruct
{
double[] a;
double[] b;
}
RetStruct myfunction(double x)
{
RetStruct s;
double[] a,b;
a~=x+1.0;
a~=x+9.0;
b~=x+2.0;
b~=x+11.0;
s.a=a;
s.b=b;
return s;
}
void main()
{
writefln("%s",myfunction(99.0));
}
Oct 15 2014
"Laeeth Isharc" <laeethnospam spammenot_laeeth.com>
Here is byref:
import std.typecons;
import std.stdio;
void myfunction(double x, ref double[] a, ref double[] b)
{
a~=x+1.0;
a~=x+9.0;
b~=x+2.0;
b~=x+11.0;
return;
}
void main()
{
double[] a;
double[] b;
myfunction(99.0,a,b);
writefln("%s %s",a,b);
}
Oct 15 2014
On Wednesday, 15 October 2014 at 16:48:24 UTC, Laeeth Isharc
wrote:
Hi.
I have to write a bunch of functions that operate on input
arrays to return multiple output arrays.
In case helpful the inputs are price bars or economic data
points (datetime, ohlc) and the outputs are nx1 arrays (I won't
say vectors) of doubles or structs.
What is the best way to return multiple arrays in this kind of
situation. In Python I returned a tuple of numpy arrays, and
the C way would be to pass a pointer to the return
destinations, and I guess I could do the same in a D way by
passing by ref not value).
I see that I can return a struct containing dynamic arrays, and
return it (by value of course). I have read the forum
discussion a while back over how to return multiple values, and
tried using tuples. I don't see that I can return a tuple of
arrays - am I missing something?
Here is a simple case. Can I do better ?
Thanks.
import std.typecons;
import std.stdio;
struct RetStruct
{
double[] a;
double[] b;
}
RetStruct myfunction(double x)
{
RetStruct s;
double[] a,b;
a~=x+1.0;
a~=x+9.0;
b~=x+2.0;
b~=x+11.0;
s.a=a;
s.b=b;
return s;
}
void main()
{
writefln("%s",myfunction(99.0));
}
You could also return an std.typecons.Tuple containing both
Oct 15 2014
On 10/15/2014 09:48 AM, Laeeth Isharc wrote:
struct RetStruct
{
double[] a;
double[] b;
}
RetStruct myfunction(double x)
That's my preference. Tuples would work as well but they have two minor
issues for me:
- Unlike a struct, the members are anonymous. (Yes, tuples members can
have names as well but not when returning or creating conveniently by
'return tuple(a, b)'.)
- Unlike Python, there is no automatic tuple expansion so one has to
refer to the members as result[0] and result[1], which is less readable
than struct members. (Yes, there is some support for tuple expansion
e.g. in foreach but it has some issues with the automatic foreach loop
counter.)
Summary: I return by struct. :)
Ali
Oct 15 2014
Thanks for the thoughts Meta and Ali. Laeeth. On Wednesday, 15 October 2014 at 17:56:06 UTC, Ali Çehreli wrote:On 10/15/2014 09:48 AM, Laeeth Isharc wrote:struct RetStruct { double[] a; double[] b; } RetStruct myfunction(double x)That's my preference. Tuples would work as well but they have two minor issues for me: - Unlike a struct, the members are anonymous. (Yes, tuples members can have names as well but not when returning or creating conveniently by 'return tuple(a, b)'.) - Unlike Python, there is no automatic tuple expansion so one has to refer to the members as result[0] and result[1], which is less readable than struct members. (Yes, there is some support for tuple expansion e.g. in foreach but it has some issues with the automatic foreach loop counter.) Summary: I return by struct. :) Ali
Oct 18 2014
On Wednesday, 15 October 2014 at 17:56:06 UTC, Ali Çehreli wrote:- Unlike a struct, the members are anonymous. (Yes, tuples members can have names as well but not when returning or creating conveniently by 'return tuple(a, b)'.)This works, but I agree it is a bit obscure (you may want to add it to your book if it's not already there): import std.typecons; Tuple!(int[], "left", int[], "right") foo(int n, int m) { return typeof(return)(new int[](n), new int[](m)); } void main() { auto res = foo(2, 3); assert(res.left.length == 2); assert(res.right.length == 3); } The problem is that D does not allow implicit conversions when returning results from a function. Tuple!(int[], int[]) is implicitly castable to Tuple!(int[], "left", int[], "right"), but you cannot return the result of tuple(new int[](n), new int[](m)) from foo(), as they are technically still different types, which would require an implicit conversion. This is (IMO) a problem; it's extremely annoying when trying to use std.typecons.Algebraic.
Oct 18 2014
On Saturday, 18 October 2014 at 14:56:06 UTC, Meta wrote:The problem is that D does not allow implicit conversions when returning results from a function."Implicit conversion" is not correct. I meant "implicit contruction".
Oct 18 2014