Re: confused with data types
Thanks for all the insights :)
Re: confused with data types
On Sunday, 18 February 2018 at 13:08:09 UTC, thorstein wrote:
On Sunday, 18 February 2018 at 12:51:04 UTC, thorstein wrote:
// Solution 1
foreach(row; arr)
{ foreach(col; row)
{ col[] *= skalar;
}
}
return arr;
// Solution 2
import std.array;
return array(arr.map!(b => array(b[].map!(c =>
array(c[].map!(d => d * skalar));
// Solution 3
import std.algorithm;
arr.each!(a => a[].each!(b => b[] *= skalar));
return arr;
Q#1:
Does the compiler optimizes all solutions equally strong or
does it prefer implementations like solution 1?
Q#2:
Solution 2 is a 1-liner but a bit harder to read. Why reducing
solution 3 to:
return arr.each!(a => a[].each!(b => b[] *= skalar));
gives a compile error? I do writeln() the function result.
Q#3:
If I can:
static import std.array;
return std.array.array(arr.map!(b =>
std.array.array(b[].map!(c =>...
How would I apply a similar version with 'static import
std.algorithm' to solution 3?
static import std.algorithm;
std.algorithm.arr.each!(a => a[]... //does obviously not work
Thanks, thorstein
Sorry, Solution 2 should be:
import std.array;
return array(arr.map!(b => array(b[].map!(c => c[] *=
skalar;
and is as readable as Solution 3. However, Q#2 still remains.
Q#1: i would guess solution 1 would be the fastest and solution 2
the slowest.
Q#2: you get a error because each returns void.
Q#3: you cant use ufcs with static imports, you have to call the
function normaly:
static import algo = std.algorithm;
algo.each!((a) => algo.each!((b) => b[] *= skalar)(a))(arr);
Re: confused with data types
On Sunday, 18 February 2018 at 12:51:04 UTC, thorstein wrote:
Thank you for the very informative answers showing different
gears in D!
However, there are still some details I'm struggling with:
Assume some calculations on a very big numeric array
'double[][][] arr'.
Now we could choose 1 out of 3 different implementations:
// Solution 1
foreach(row; arr)
{ foreach(col; row)
{ col[] *= skalar;
}
}
return arr;
// Solution 2
import std.array;
return array(arr.map!(b => array(b[].map!(c => array(c[].map!(d
=> d * skalar));
// Solution 3
import std.algorithm;
arr.each!(a => a[].each!(b => b[] *= skalar));
return arr;
Q#1:
Does the compiler optimizes all solutions equally strong or
does it prefer implementations like solution 1?
Q#2:
Solution 2 is a 1-liner but a bit harder to read. Why reducing
solution 3 to:
return arr.each!(a => a[].each!(b => b[] *= skalar));
gives a compile error? I do writeln() the function result.
Q#3:
If I can:
static import std.array;
return std.array.array(arr.map!(b => std.array.array(b[].map!(c
=>...
How would I apply a similar version with 'static import
std.algorithm' to solution 3?
static import std.algorithm;
std.algorithm.arr.each!(a => a[]... //does obviously not work
Thanks, thorstein
Sorry, Solution 2 should be:
import std.array;
return array(arr.map!(b => array(b[].map!(c => c[] *= skalar;
and is as readable as Solution 3. However, Q#2 still remains.
Re: confused with data types
Thank you for the very informative answers showing different
gears in D!
However, there are still some details I'm struggling with:
Assume some calculations on a very big numeric array
'double[][][] arr'.
Now we could choose 1 out of 3 different implementations:
// Solution 1
foreach(row; arr)
{ foreach(col; row)
{ col[] *= skalar;
}
}
return arr;
// Solution 2
import std.array;
return array(arr.map!(b => array(b[].map!(c => array(c[].map!(d
=> d * skalar));
// Solution 3
import std.algorithm;
arr.each!(a => a[].each!(b => b[] *= skalar));
return arr;
Q#1:
Does the compiler optimizes all solutions equally strong or does
it prefer implementations like solution 1?
Q#2:
Solution 2 is a 1-liner but a bit harder to read. Why reducing
solution 3 to:
return arr.each!(a => a[].each!(b => b[] *= skalar));
gives a compile error? I do writeln() the function result.
Q#3:
If I can:
static import std.array;
return std.array.array(arr.map!(b => std.array.array(b[].map!(c
=>...
How would I apply a similar version with 'static import
std.algorithm' to solution 3?
static import std.algorithm;
std.algorithm.arr.each!(a => a[]... //does obviously not work
Thanks, thorstein
Re: confused with data types
double[][] skalar_m_2d(double[][] arr, double skalar)
{
import std.algorithm;
// return arr.map(a=> a[] *= skalar).array;
arr.each!((ref a) => a[] *= skalar));
return arr;
}
Re: confused with data types
On Saturday, 17 February 2018 at 16:12:48 UTC, thorstein wrote:
public double[][] skalar_m_2d(double[][] array, double skalar)
{
return array.map!(b => b[].map!(c => c * skalar));
}
It'd probably be better to just do that in-place...
foreach(row; array)
row[] *= skalar;
return array;
Note that'd overwrite the existing data though. But the compiler
could more aggressively optimize that than the individual maps.
How can I get the result as double[][] ???
But if you do need the double[][] type exactly as well as a new
copy instead of editing the one you have, you can:
static import std.array;
return std.array.array(array.map!(b => std.array.array(b[].map!(c
=> c * skalar;
The std.array.array function copies the return value of functions
like `map` into a new array. It is called twice here because
double[][] is an array of arrays.
(the word "array" is used way too much there lol)
The reason map doesn't do this automatically btw is because
copying the arrays can be somewhat expensive, so it doesn't force
you to do work you don't often need.
Re: confused with data types
On Saturday, 17 February 2018 at 16:12:48 UTC, thorstein wrote:
Hello,
This was my goal:
-
public double[][] skalar_m_2d(double[][] array, double skalar)
{
return array.map!(b => b[].map!(c => c * skalar));
}
!!! But: return value is not double!
Type check for return value:
a = array.map!(b => b[].map!(c => c * skalar))
writeln(typeof(a).stringof); //-> MapResult!("__lambda4,
double[][])
a = array.map!(b => b[].map!(c => c * skalar))[1];
writeln(typeof(a).stringof); //-> MapResult!("__lambda2,
double[])
How can I get the result as double[][] ???
Thanks, thorstein
I'm no expert, but importing std.array and doing a.array() should
work.
confused with data types
Hello,
This was my goal:
-
public double[][] skalar_m_2d(double[][] array, double skalar)
{
return array.map!(b => b[].map!(c => c * skalar));
}
!!! But: return value is not double!
Type check for return value:
a = array.map!(b => b[].map!(c => c * skalar))
writeln(typeof(a).stringof); //-> MapResult!("__lambda4,
double[][])
a = array.map!(b => b[].map!(c => c * skalar))[1];
writeln(typeof(a).stringof); //-> MapResult!("__lambda2, double[])
How can I get the result as double[][] ???
Thanks, thorstein
