merging a group result
Hi all,
I'm looking for a d-ish way to solve a basic
"split-apply-combine" workflow. The idea is described (and
solved) here:
https://stackoverflow.com/questions/39922986/pandas-group-by-and-sum
So, given a structure with some fields, say
´´´
struct S
{
string s;
int i;
}
´´´
I create an array of them, like
´´´
void main()
{
import std.experimental.all;
S[] sarr;
sarr.length = 6;
sarr[0].s = "a";
sarr[1].s = "a";
sarr[2].s = "b";
sarr[3].s = "b";
sarr[4].s = "c";
sarr[5].s = "c";
sarr[0].i = 1;
sarr[1].i = 2;
sarr[2].i = 4;
sarr[3].i = 8;
sarr[4].i = 16;
sarr[5].i = 32;
auto res = sarr.group!((a, b) => a.s == b.s);
//writeln(res);
}
´´´
I'm also able to group them by a field, see last line.
But now the problems begin:
- The group operation tries to use the structure itself as a key,
despite I provide a custom binary predicate.
- I could ignore the fact above, but how, given the result of the
grouping operation I can merge by some function (like sum) the
group results?
At this moment, I assume, that I'm approaching the problem from
the wrong end, and simply don't see something trivial... Anyway,
does anybody has a hint for me?
Re: How to get an inout constructor working with a template wrapper
On Sunday, 22 July 2018 at 23:11:09 UTC, Ali Çehreli wrote:
Without much confidence on my side, first, I think you need to
make the constructor parameter inout(T) as well. Otherwise, you
may be making a const(W!T) initialized with a non-const T.
After that, I like the "type constructor" syntax in main_alt()
below (which works) but a better approach is to use a
convenience function like wrap() below:
struct W(T) {
T val;
this(inout(T) val) inout {
this.val = val;
}
}
class C {}
void main_alt() {
auto a = W!C(new C);
auto b = immutable W!(immutable C)(new C);
}
auto wrap(T)(inout T t) {
return inout(W!T)(t);
}
void main() {
auto a = wrap(new C);
auto b = wrap(new immutable(C));
}
Ali
"taklitlerinden sakınınız" :o)
Thank you Ali! That helped :) I've gotten most of it sorted out
now, and the factory wrap is definitely the way to go, it also
turned out that inout(T) and inout T (so inout without parens)
was surprisingly different (maybe it's a bug? - to test you can
remove the parens around U on line 3 in this sample:
https://run.dlang.io/is/gd5oxW
Also over there, line 24:
auto si = wrap!(immutable int)(3);
seems to be giving problems. Any ideas there? Error is:
onlineapp.d(8): Error: inout on return means inout must be on a
parameter as well for pure nothrow @nogc @safe
inout(W!(immutable(int)))(immutable(int) t)
onlineapp.d(23): Error: template instance
`onlineapp.wrap!(immutable(int))` error instantiating
To make it compile successfully you can either:
1) Chance immutable to const, then it works for some reason.
2) Change the line to: "auto si = wrap(cast(immutable int)3);" -
i.e. do not explicitly provide type information.
Cheers,
- Ali
Re: merging a group result
On 23/07/2018 11:49 PM, Alex wrote: At this moment, I assume, that I'm approaching the problem from the wrong end, and simply don't see something trivial... Anyway, does anybody has a hint for me? Map the range to the integer value, then sum it.
Re: How to get an inout constructor working with a template wrapper
On Monday, 23 July 2018 at 12:02:58 UTC, aliak wrote: https://run.dlang.io/is/gd5oxW Sorry wrong link! This one is correct -> https://run.dlang.io/is/azxmGN
Re: merging a group result
On Monday, 23 July 2018 at 11:49:58 UTC, Alex wrote:
Hi all,
I'm looking for a d-ish way to solve a basic
"split-apply-combine" workflow. The idea is described (and
solved) here:
https://stackoverflow.com/questions/39922986/pandas-group-by-and-sum
So, given a structure with some fields, say
´´´
struct S
{
string s;
int i;
}
´´´
I create an array of them, like
´´´
void main()
{
import std.experimental.all;
S[] sarr;
sarr.length = 6;
sarr[0].s = "a";
sarr[1].s = "a";
sarr[2].s = "b";
sarr[3].s = "b";
sarr[4].s = "c";
sarr[5].s = "c";
sarr[0].i = 1;
sarr[1].i = 2;
sarr[2].i = 4;
sarr[3].i = 8;
sarr[4].i = 16;
sarr[5].i = 32;
auto res = sarr.group!((a, b) => a.s == b.s);
//writeln(res);
}
´´´
I'm also able to group them by a field, see last line.
But now the problems begin:
- The group operation tries to use the structure itself as a
key, despite I provide a custom binary predicate.
- I could ignore the fact above, but how, given the result of
the grouping operation I can merge by some function (like sum)
the group results?
At this moment, I assume, that I'm approaching the problem from
the wrong end, and simply don't see something trivial...
Anyway, does anybody has a hint for me?
You could use chunkBy:
auto res = sarr.chunkBy!((a, b) => a.s == b.s).map!(a =>
tuple(a.front.s, a.map!(b => b.i).sum));
https://run.dlang.io/is/TJOEmf
chunkBy:
---
[S("a", 1), S("a", 2)]
[S("b", 4), S("b", 8)]
[S("c", 16), S("c", 32)]
---
group:
---
Tuple!(S, uint)(const(S)("a", 1), 2)
Tuple!(S, uint)(const(S)("b", 4), 2)
Tuple!(S, uint)(const(S)("c", 16), 2)
---
Re: merging a group result
On Monday, 23 July 2018 at 12:07:37 UTC, Seb wrote: You could use chunkBy: auto res = sarr.chunkBy!((a, b) => a.s == b.s).map!(a => tuple(a.front.s, a.map!(b => b.i).sum)); https://run.dlang.io/is/TJOEmf Ha... This helps! Thanks a lot! :)
Re: QWebView requesting QtE5WebEng32.so on windows
On Saturday, 21 July 2018 at 19:11:08 UTC, Dr.No wrote: So I went to try out QWebView on Windows from this wrapper: https://github.com/MGWL/QtE5 all the examples went fine until I tried QWebView: Prior to version Qt-5.5 WebKit was used, and for later versions of chromium-based WebEngine. You probably have a WebKit-based version and need to use: Loader(dll.Qt5widgets + dll.QtE5Web, true)). LoadQt (...) for Windows 32/64 WebEngine contains a typo ... Must be DLL
Re: How to get an inout constructor working with a template wrapper
On Monday, 23 July 2018 at 12:02:58 UTC, aliak wrote:
Thank you Ali! That helped :) I've gotten most of it sorted out
now, and the factory wrap is definitely the way to go, it also
turned out that inout(T) and inout T (so inout without parens)
was surprisingly different (maybe it's a bug? - to test you can
remove the parens around U on line 3 in this sample:
https://run.dlang.io/is/gd5oxW
Also over there, line 24:
auto si = wrap!(immutable int)(3);
Both of these seem to work (as you pointed out)
// immutable(W!int)
auto si = wrap!(int)(cast(immutable)3); // or
wrap(cast(immutable)3);
// W!(immutable(int))
auto si2 = W!(immutable int)(3);
seems to be giving problems. Any ideas there? Error is:
onlineapp.d(8): Error: inout on return means inout must be on a
parameter as well for pure nothrow @nogc @safe
inout(W!(immutable(int)))(immutable(int) t)
onlineapp.d(23): Error: template instance
`onlineapp.wrap!(immutable(int))` error instantiating
To make it compile successfully you can either:
1) Chance immutable to const, then it works for some reason.
2) Change the line to: "auto si = wrap(cast(immutable int)3);"
- i.e. do not explicitly provide type information.
I don't know why
wrap!(immutable int)(3);
is not working. The error message
"Error: inout on return means inout must be on a parameter as
well for pure nothrow @nogc @safe
inout(W!(immutable(int)))(return immutable(int) t)"
sounds very odd and not at all helpful, at least regarding that
removing immutable from the template argument works.
Cheers,
- Ali
The depths of D. Why does the following only work with "return
ref"?
struct W(T) {
T val;
this(U : T)(auto ref inout U val) inout {
pragma(msg, typeof(val));
this.val = val;
}
}
// Fails without "return ref" (escaping t warning...)
auto wrap(T)(return ref inout T t) {
return inout W!T(t);
}
class C {}
void main() {
immutable C ci = new immutable C;
auto i = wrap(im);
pragma(msg, typeof(i));
}
How to avoid inout type constructor with Optional type wrapper undoing string type
Hi,
I'm playing around with an Optional wrapper type. It stores a
type T and a bool that defines whether a value is defined or not:
struct Optional(T) {
T value;
bool defined = false;
this(U : T)(auto ref inout(U) value) inout {
this.value = value;
this.defined = true;
}
}
To facilitate it's use I have two type constructors:
inout(Optional!T) some(T)(auto ref inout(T) value) {
return inout(Optional!T)(value);
}
Optional!T no(T)() {
return Optional!T();
}
The above produces a problem when working with strings. Basically
the type information gets slightly altered so you can't do this:
auto a = [no!string, some("hello")];
You get a type mismatch:
* no!string = Optional!string
* some("hello") = immutable(Optional!(char[]))
I've created a short code gist, so basically I'm wondering how to
get it to compile without changing what's in main()
https://run.dlang.io/is/BreNdZ
I guess I can specialize on string type T, but this is a more
general problem that can be shown with:
struct S {}
alias Thing = immutable S;
Thing thing = S();
auto x = some(thing);
auto y = no!Thing;
auto arr = [x, y]; // no can do buddy
Cheers,
- Ali
Re: How to avoid inout type constructor with Optional type wrapper undoing string type
On 2018-07-23 20:39, aliak wrote:
Hi,
I'm playing around with an Optional wrapper type. It stores a type T and
a bool that defines whether a value is defined or not:
struct Optional(T) {
T value;
bool defined = false;
this(U : T)(auto ref inout(U) value) inout {
this.value = value;
this.defined = true;
}
}
To facilitate it's use I have two type constructors:
inout(Optional!T) some(T)(auto ref inout(T) value) {
return inout(Optional!T)(value);
}
Optional!T no(T)() {
return Optional!T();
}
The above produces a problem when working with strings. Basically the
type information gets slightly altered so you can't do this:
auto a = [no!string, some("hello")];
You get a type mismatch:
* no!string = Optional!string
* some("hello") = immutable(Optional!(char[]))
I've created a short code gist, so basically I'm wondering how to get it
to compile without changing what's in main()
https://run.dlang.io/is/BreNdZ
I guess I can specialize on string type T, but this is a more general
problem that can be shown with:
struct S {}
alias Thing = immutable S;
Thing thing = S();
auto x = some(thing);
auto y = no!Thing;
auto arr = [x, y]; // no can do buddy
This [1] compiles the first example but not the second.
[1] https://run.dlang.io/is/SJ02kP
--
/Jacob Carlborg
Re: How to avoid inout type constructor with Optional type wrapper undoing string type
On Monday, 23 July 2018 at 19:02:02 UTC, Jacob Carlborg wrote: This [1] compiles the first example but not the second. [1] https://run.dlang.io/is/SJ02kP Aye it does, but it also sets T to always const which is unfortunately impractical for my use case :(
Re: How to avoid inout type constructor with Optional type wrapper undoing string type
On Monday, 23 July 2018 at 19:22:13 UTC, aliak wrote:
On Monday, 23 July 2018 at 19:02:02 UTC, Jacob Carlborg wrote:
This [1] compiles the first example but not the second.
[1] https://run.dlang.io/is/SJ02kP
Aye it does, but it also sets T to always const which is
unfortunately impractical for my use case :(
Ok, now I'm totally confused. Defining an extra type constructor
makes everything work. I.e add a const one to the inout one:
auto defined(T)(const auto ref T value) {
return W!T(value);
}
and everything works!
Can anyone say why that is?
Re: How to avoid inout type constructor with Optional type wrapper undoing string type
On Monday, 23 July 2018 at 19:31:42 UTC, aliak wrote:
Ok, now I'm totally confused. Defining an extra type
constructor makes everything work. I.e add a const one to the
inout one:
auto defined(T)(const auto ref T value) {
return W!T(value);
}
and everything works!
Can anyone say why that is?
Boh, seems other problems crop up now as doing this:
auto a = defined!(int*)(null);
produces error:
onlineapp.d(13): Error: inout constructor
onlineapp.W!(int*).W.__ctor!(int*).this creates const object, not
mutable
onlineapp.d(30): Error: template instance
`onlineapp.defined!(int*)` error instantiating
https://run.dlang.io/is/BWYxA8
trait to get the body code of a function?
Hello, __traits and std.traits already offer access to function information like input parameters, e.g. in std.traits: ParameterIdentifierTuple ParameterStorageClassTuple Even if that might sound strange, is there a compile time access to the body of the function, e.g. as a code string, or at least to the filename where it was declared? I have not found a direct "string" access, but I found these: https://dlang.org/phobos/std_traits.html#moduleName https://dlang.org/phobos/std_traits.html#packageName ...and I am not sure how to proceed from here to get the code as a string that declared the function. Context: I have some compile-time ideas in mind (code transformation). Best regards, Guillaume Lathoud
Re: trait to get the body code of a function?
On 24/07/2018 4:43 PM, Guillaume Lathoud wrote: Hello, __traits and std.traits already offer access to function information like input parameters, e.g. in std.traits: ParameterIdentifierTuple ParameterStorageClassTuple Even if that might sound strange, is there a compile time access to the body of the function, e.g. as a code string, or at least to the filename where it was declared? I have not found a direct "string" access, but I found these: https://dlang.org/phobos/std_traits.html#moduleName https://dlang.org/phobos/std_traits.html#packageName ...and I am not sure how to proceed from here to get the code as a string that declared the function. Context: I have some compile-time ideas in mind (code transformation). Best regards, Guillaume Lathoud Doesn't exist.
