Re: Arrays - Inserting and moving data
MattCodr wrote: I have a doubt about the best way to insert and move (not replace) some data on an array. I have the vision, that a mapping from a dense range of integers to some value type and wast (i.e. Theta( n)) changes of this mapping are a severe hint for a maldesign. -manfred
Re: Arrays - Inserting and moving data
On 11 February 2012 10:45, Jonathan M Davis jmdavisp...@gmx.com wrote:
On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
I know that feeling. I had no exposure to functional programming and
options like chain never come to my head. Although map is a concept that
I made friends with early.
It would benefit your programming in general to learn a functional programming
language and become reasonably proficient in it, even if you don't intend to
program in it normally. It'll increase the number of tools in your programming
toolbox and improve your programming in other programming languages. It's
something that not enough programmers get sufficient exposure to IMHO.
- Jonathan M Davis
I found that learning Haskell made me significantly better at what I
do. New paradigms are good for reminding you to think outside the box,
I also learnt Prolog for a university course (AI) and that was an
interesting challenge. Logical programming, where you define the
boundaries of the program and then it works out the possible answers
for you, amazingly useful for BNF grammars and similar constructs.
If fact it's got to the point where I feel hamstrung if I can't do at
least function passing (fortunately C, C++ and D can do this), and I
prefer to work with languages that support closures and anonymous
functions, since you can do wonders with simple constructs like map,
fold (reduce) and filter. In fact a naive implementation of quicksort
can be done succinctly in any language that supports filter.
T[] sort(T)(T[] array) {
pivot = array[array.length/2];
return sort(filter!(a ~pivot)(array)~pivot~sort(filter!(a
~pivot)(array));
}
(Disclaimer, this is probably a very slow implementation, possibly
very broken, may cause compiler demons to possess your computer, DO
NOT USE!)
I have left out some details for brevity, and it probably won't work
in alot of situations, but it demonstrates the power of functional
programming, quicksort in 4 lines (sort of, its not like Haskell's
quicksort in 2 lines is any better mind you, its slow as balls
because of all the memory allocation it has to do).
Anyway, yay for functional programming and thread derailment.
James
Re: Arrays - Inserting and moving data
On 02/13/2012 03:19 PM, James Miller wrote:
On 11 February 2012 10:45, Jonathan M Davisjmdavisp...@gmx.com wrote:
On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
I know that feeling. I had no exposure to functional programming and
options like chain never come to my head. Although map is a concept that
I made friends with early.
It would benefit your programming in general to learn a functional programming
language and become reasonably proficient in it, even if you don't intend to
program in it normally. It'll increase the number of tools in your programming
toolbox and improve your programming in other programming languages. It's
something that not enough programmers get sufficient exposure to IMHO.
- Jonathan M Davis
I found that learning Haskell made me significantly better at what I
do. New paradigms are good for reminding you to think outside the box,
I also learnt Prolog for a university course (AI) and that was an
interesting challenge. Logical programming, where you define the
boundaries of the program and then it works out the possible answers
for you, amazingly useful for BNF grammars and similar constructs.
If fact it's got to the point where I feel hamstrung if I can't do at
least function passing (fortunately C, C++ and D can do this), and I
prefer to work with languages that support closures and anonymous
functions, since you can do wonders with simple constructs like map,
fold (reduce) and filter. In fact a naive implementation of quicksort
can be done succinctly in any language that supports filter.
T[] sort(T)(T[] array) {
pivot = array[array.length/2];
return sort(filter!(a ~pivot)(array)~pivot~sort(filter!(a
~pivot)(array));
}
(Disclaimer, this is probably a very slow implementation, possibly
very broken, may cause compiler demons to possess your computer, DO
NOT USE!)
I have left out some details for brevity, and it probably won't work
in alot of situations, but it demonstrates the power of functional
programming, quicksort in 4 lines (sort of, its not like Haskell's
quicksort in 2 lines is any better mind you, its slow as balls
because of all the memory allocation it has to do).
Anyway, yay for functional programming and thread derailment.
James
If it is slow and uses an awful lot of auxiliary memory it is not
quicksort as much as it may conceptually resemble quicksort. Try to
implement in-place quicksort in Haskell. It will look like C code. Also
see:
http://stackoverflow.com/questions/5268156/how-do-you-do-an-in-place-quicksort-in-haskell
Re: Arrays - Inserting and moving data
On 14 February 2012 06:25, Timon Gehr timon.g...@gmx.ch wrote:
On 02/13/2012 03:19 PM, James Miller wrote:
On 11 February 2012 10:45, Jonathan M Davisjmdavisp...@gmx.com wrote:
On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
I know that feeling. I had no exposure to functional programming and
options like chain never come to my head. Although map is a concept
that
I made friends with early.
It would benefit your programming in general to learn a functional
programming
language and become reasonably proficient in it, even if you don't intend
to
program in it normally. It'll increase the number of tools in your
programming
toolbox and improve your programming in other programming languages. It's
something that not enough programmers get sufficient exposure to IMHO.
- Jonathan M Davis
I found that learning Haskell made me significantly better at what I
do. New paradigms are good for reminding you to think outside the box,
I also learnt Prolog for a university course (AI) and that was an
interesting challenge. Logical programming, where you define the
boundaries of the program and then it works out the possible answers
for you, amazingly useful for BNF grammars and similar constructs.
If fact it's got to the point where I feel hamstrung if I can't do at
least function passing (fortunately C, C++ and D can do this), and I
prefer to work with languages that support closures and anonymous
functions, since you can do wonders with simple constructs like map,
fold (reduce) and filter. In fact a naive implementation of quicksort
can be done succinctly in any language that supports filter.
T[] sort(T)(T[] array) {
pivot = array[array.length/2];
return sort(filter!(a ~pivot)(array)~pivot~sort(filter!(a
~pivot)(array));
}
(Disclaimer, this is probably a very slow implementation, possibly
very broken, may cause compiler demons to possess your computer, DO
NOT USE!)
I have left out some details for brevity, and it probably won't work
in alot of situations, but it demonstrates the power of functional
programming, quicksort in 4 lines (sort of, its not like Haskell's
quicksort in 2 lines is any better mind you, its slow as balls
because of all the memory allocation it has to do).
Anyway, yay for functional programming and thread derailment.
James
If it is slow and uses an awful lot of auxiliary memory it is not quicksort
as much as it may conceptually resemble quicksort. Try to implement in-place
quicksort in Haskell. It will look like C code. Also see:
http://stackoverflow.com/questions/5268156/how-do-you-do-an-in-place-quicksort-in-haskell
It is still conceptually quicksort, the divide-and-conquer method
based on partitioning the list. I wasn't writing it to show a valid
implementation (I didn't even test it, it probably doesn't compile), I
even warned of compiler demons! Its a demonstration of the
succinctness of functional techniques for certain problems, not a show
that functional languages are teh awesum and all other langauges
suck. Haskell is almost a pure functional language, therefore, under
normal circumstances, every change to the array will allocate a new
array, this is because of the whole immutability thing that it has
going on. Of course I would never use such an implementation in real
life, and Haskellers tend to avoid algorithms that do these kinds of
things, using sorts like mergesort instead.
Saying it is not quicksort as much as it may conceptually resemble
quicksort is kinda odd, its like saying it is not a car, as much as
it may conceptually resemble a car because it doesn't run on petrol
or gas, but instead runs on environment destroying orphan tears.
James Miller
Re: Arrays - Inserting and moving data
On 02/13/2012 03:34 PM, James Miller wrote: Saying it is not quicksort as much as it may conceptually resemble quicksort is kinda odd, its like saying it is not a car, as much as it may conceptually resemble a car because it doesn't run on petrol or gas, but instead runs on environment destroying orphan tears. For what its worth, Andrei uses that argument in his On Iteration article with For starters, [one implementation of Haskell's] qsort is not really quicksort. Quicksort, as defined by Hoare in his seminal paper [8], is an in-place algorithm. http://www.informit.com/articles/printerfriendly.aspx?p=1407357 Ali
Re: Arrays - Inserting and moving data
On 14 February 2012 12:45, Ali Çehreli acehr...@yahoo.com wrote: On 02/13/2012 03:34 PM, James Miller wrote: Saying it is not quicksort as much as it may conceptually resemble quicksort is kinda odd, its like saying it is not a car, as much as it may conceptually resemble a car because it doesn't run on petrol or gas, but instead runs on environment destroying orphan tears. For what its worth, Andrei uses that argument in his On Iteration article with For starters, [one implementation of Haskell's] qsort is not really quicksort. Quicksort, as defined by Hoare in his seminal paper [8], is an in-place algorithm. http://www.informit.com/articles/printerfriendly.aspx?p=1407357 Ali Fair enough, I didn't realise that Quicksort was defined as in place, in that case, I retract my opposition to not really a quicksort however my missing the point still stands. I still prefer arrays over S-lists anyway, how else do I efficiently implement a heap?
Re: Arrays - Inserting and moving data
On Tuesday, February 14, 2012 13:02:43 James Miller wrote: On 14 February 2012 12:45, Ali Çehreli acehr...@yahoo.com wrote: On 02/13/2012 03:34 PM, James Miller wrote: Saying it is not quicksort as much as it may conceptually resemble quicksort is kinda odd, its like saying it is not a car, as much as it may conceptually resemble a car because it doesn't run on petrol or gas, but instead runs on environment destroying orphan tears. For what its worth, Andrei uses that argument in his On Iteration article with For starters, [one implementation of Haskell's] qsort is not really quicksort. Quicksort, as defined by Hoare in his seminal paper [8], is an in-place algorithm. http://www.informit.com/articles/printerfriendly.aspx?p=1407357 Ali Fair enough, I didn't realise that Quicksort was defined as in place, in that case, I retract my opposition to not really a quicksort however my missing the point still stands. I still prefer arrays over S-lists anyway, how else do I efficiently implement a heap? Orphan tears. It's the only way to go. - Jonathan M Davis
Re: Arrays - Inserting and moving data
On 02/14/2012 12:34 AM, James Miller wrote:
On 14 February 2012 06:25, Timon Gehrtimon.g...@gmx.ch wrote:
On 02/13/2012 03:19 PM, James Miller wrote:
On 11 February 2012 10:45, Jonathan M Davisjmdavisp...@gmx.comwrote:
On Friday, February 10, 2012 13:32:56 Marco Leise wrote:
I know that feeling. I had no exposure to functional programming and
options like chain never come to my head. Although map is a concept
that
I made friends with early.
It would benefit your programming in general to learn a functional
programming
language and become reasonably proficient in it, even if you don't intend
to
program in it normally. It'll increase the number of tools in your
programming
toolbox and improve your programming in other programming languages. It's
something that not enough programmers get sufficient exposure to IMHO.
- Jonathan M Davis
I found that learning Haskell made me significantly better at what I
do. New paradigms are good for reminding you to think outside the box,
I also learnt Prolog for a university course (AI) and that was an
interesting challenge. Logical programming, where you define the
boundaries of the program and then it works out the possible answers
for you, amazingly useful for BNF grammars and similar constructs.
If fact it's got to the point where I feel hamstrung if I can't do at
least function passing (fortunately C, C++ and D can do this), and I
prefer to work with languages that support closures and anonymous
functions, since you can do wonders with simple constructs like map,
fold (reduce) and filter. In fact a naive implementation of quicksort
can be done succinctly in any language that supports filter.
T[] sort(T)(T[] array) {
pivot = array[array.length/2];
return sort(filter!(a~pivot)(array)~pivot~sort(filter!(a
~pivot)(array));
}
(Disclaimer, this is probably a very slow implementation, possibly
very broken, may cause compiler demons to possess your computer, DO
NOT USE!)
I have left out some details for brevity, and it probably won't work
in alot of situations, but it demonstrates the power of functional
programming, quicksort in 4 lines (sort of, its not like Haskell's
quicksort in 2 lines is any better mind you, its slow as balls
because of all the memory allocation it has to do).
Anyway, yay for functional programming and thread derailment.
James
If it is slow and uses an awful lot of auxiliary memory it is not quicksort
as much as it may conceptually resemble quicksort. Try to implement in-place
quicksort in Haskell. It will look like C code. Also see:
http://stackoverflow.com/questions/5268156/how-do-you-do-an-in-place-quicksort-in-haskell
It is still conceptually quicksort, the divide-and-conquer method
based on partitioning the list.
Hoare's original quicksort algorithm is more detailed than what is
sketched here. The main point is the in-place partition operation with
the two pointers approaching each other.
I wasn't writing it to show a valid
implementation (I didn't even test it, it probably doesn't compile), I
even warned of compiler demons! Its a demonstration of the
succinctness of functional techniques for certain problems, not a show
that functional languages are teh awesum and all other langauges
suck.
The approach given does not solve the problem (it does not implement
Quicksort). Quicksort in Haskell looks like Quicksort in D, because the
algorithm depends on destructive updates. Functional techniques can be
succinct for certain problems, but implementing Quicksort is not one of
them.
Haskell is almost a pure functional language, therefore, under
normal circumstances, every change to the array will allocate a new
array,
Haskell can do destructive array updates that look like pure operations
just fine.
http://hackage.haskell.org/packages/archive/array/0.2.0.0/doc/html/Data-Array-MArray.html
this is because of the whole immutability thing that it has going on.
This is confusing the abstraction with its implementation. It is
impossible to recreate Haskell's execution semantics in D using only
immutable types.
Of course I would never use such an implementation in real
life, and Haskellers tend to avoid algorithms that do these kinds of
things, using sorts like mergesort instead.
Mostly lazy mergesort if I'm not mistaken. And they don't usually use it
to sort arrays, they sort lists. Haskell arrays ought to be sorted with
introsort if the comparison operation is cheap.
Saying it is not quicksort as much as it may conceptually resemble
quicksort is kinda odd, its like saying it is not a car, as much as
it may conceptually resemble a car because it doesn't run on petrol
or gas, but instead runs on environment destroying orphan tears.
It is more like saying a handcart is not a car, as much as it may
conceptually resemble a car (the engine is missing!).
Re: Arrays - Inserting and moving data
Am 09.02.2012, 22:03 Uhr, schrieb MattCodr matheus_...@hotmail.com: On Thursday, 9 February 2012 at 19:49:43 UTC, Timon Gehr wrote: Note that this code does the same, but is more efficient if you don't actually need the array: Yes I know, In fact I need re-think the way I code with this new features of D, like ranges for example. Thanks, Matheus. I know that feeling. I had no exposure to functional programming and options like chain never come to my head. Although map is a concept that I made friends with early.
Re: Arrays - Inserting and moving data
On Friday, February 10, 2012 13:32:56 Marco Leise wrote: I know that feeling. I had no exposure to functional programming and options like chain never come to my head. Although map is a concept that I made friends with early. It would benefit your programming in general to learn a functional programming language and become reasonably proficient in it, even if you don't intend to program in it normally. It'll increase the number of tools in your programming toolbox and improve your programming in other programming languages. It's something that not enough programmers get sufficient exposure to IMHO. - Jonathan M Davis
Re: Arrays - Inserting and moving data
I __believe__ that insertInPlace doesn't shift the elements, but use an
appender allocating another array instead.
Maybe this function do what you want.
int[] arr = [0,1,2,3,4,5,6,7,8,9];
void maybe(T)(T[] arr, size_t pos, T value) {
size_t i;
for (i = arr.length - 1; i pos; i--) {
arr[i] = arr[i-1];
}
arr[i] = value;
}
maybe(arr, 3, 0);
maybe(arr, 0, 1);
assert(arr == [1, 0, 1, 2, 0, 3, 4, 5, 6, 7]);
2012/2/9 MattCodr matheus_...@hotmail.com
I have a doubt about the best way to insert and move (not replace) some
data on an array.
For example,
In some cases if I want to do action above, I do a loop moving the data
until the point that I want and finally I insert the new data there.
In D I did this:
begin code
.
.
.
int[] arr = [0,1,2,3,4,5,6,7,8,9];
arr.insertInPlace(position, newValue);
arr.popBack();
.
.
.
end code
After the insertInPlace my array changed it's length to 11, so I use
arr.popBack(); to keep the array length = 10;
The code above is working well, I just want know if is there a better way?
Thanks,
Matheus.
Re: Arrays - Inserting and moving data
On Thursday, 9 February 2012 at 12:51:09 UTC, Pedro Lacerda wrote:
I __believe__ that insertInPlace doesn't shift the elements,
Yes, It appears that it really doesn't shift the array,
insertInPlace just returns a new array with a new element in n
position.
Maybe this function do what you want.
int[] arr = [0,1,2,3,4,5,6,7,8,9];
void maybe(T)(T[] arr, size_t pos, T value) {
size_t i;
for (i = arr.length - 1; i pos; i--) {
arr[i] = arr[i-1];
}
arr[i] = value;
}
In fact, I usually wrote functions as you did. I just looking for
a new way to do that with D and Phobos lib.
Thanks,
Matheus.
Re: Arrays - Inserting and moving data
On 02/09/2012 03:47 AM, MattCodr wrote:
I have a doubt about the best way to insert and move (not replace) some
data on an array.
For example,
In some cases if I want to do action above, I do a loop moving the data
until the point that I want and finally I insert the new data there.
In D I did this:
begin code
.
.
.
int[] arr = [0,1,2,3,4,5,6,7,8,9];
arr.insertInPlace(position, newValue);
arr.popBack();
.
.
.
end code
After the insertInPlace my array changed it's length to 11, so I use
arr.popBack(); to keep the array length = 10;
The code above is working well, I just want know if is there a better way?
Thanks,
Matheus.
Most straightforward that I know of is the following:
arr = arr[0 .. position] ~ [ newValue ] ~ arr[position + 1 .. $];
But if you don't actually want to modify the data, you can merely access
the elements in-place by std.range.chain:
import std.stdio;
import std.range;
void main()
{
int[] arr = [0,1,2,3,4,5,6,7,8,9];
immutable position = arr.length / 2;
immutable newValue = 42;
auto r = chain(arr[0 .. position], [ newValue ], arr[position + 1
.. $]);
writeln(r);
}
'r' above is a lazy range that just provides access to the three ranges
given to it. 'arr' does not change in any way.
Ali
Re: Arrays - Inserting and moving data
On Thu, Feb 09, 2012 at 10:30:22AM -0800, Ali Çehreli wrote:
[...]
But if you don't actually want to modify the data, you can merely
access the elements in-place by std.range.chain:
import std.stdio;
import std.range;
void main()
{
int[] arr = [0,1,2,3,4,5,6,7,8,9];
immutable position = arr.length / 2;
immutable newValue = 42;
auto r = chain(arr[0 .. position], [ newValue ], arr[position +
1 .. $]);
writeln(r);
}
'r' above is a lazy range that just provides access to the three
ranges given to it. 'arr' does not change in any way.
[...]
Wow! This is really cool. So you *can* have O(1) insertions in the
middle of an array after all. :)
Of course, you probably want to flatten it once in a while to keep
random access cost from skyrocketing. (I'm assuming delegates or
something equivalent are involved in generating the lazy range?)
T
--
Give a man a fish, and he eats once. Teach a man to fish, and he will sit
forever.
Re: Arrays - Inserting and moving data
On Thursday, 9 February 2012 at 18:30:22 UTC, Ali Çehreli wrote:
On 02/09/2012 03:47 AM, MattCodr wrote:
I have a doubt about the best way to insert and move (not
replace) some
data on an array.
For example,
In some cases if I want to do action above, I do a loop moving
the data
until the point that I want and finally I insert the new data
there.
In D I did this:
begin code
.
.
.
int[] arr = [0,1,2,3,4,5,6,7,8,9];
arr.insertInPlace(position, newValue);
arr.popBack();
.
.
.
end code
After the insertInPlace my array changed it's length to 11, so
I use
arr.popBack(); to keep the array length = 10;
The code above is working well, I just want know if is there a
better way?
Thanks,
Matheus.
Most straightforward that I know of is the following:
arr = arr[0 .. position] ~ [ newValue ] ~ arr[position + 1
.. $];
But if you don't actually want to modify the data, you can
merely access the elements in-place by std.range.chain:
import std.stdio;
import std.range;
void main()
{
int[] arr = [0,1,2,3,4,5,6,7,8,9];
immutable position = arr.length / 2;
immutable newValue = 42;
auto r = chain(arr[0 .. position], [ newValue ],
arr[position + 1 .. $]);
writeln(r);
}
'r' above is a lazy range that just provides access to the
three ranges given to it. 'arr' does not change in any way.
Ali
Hi Ali,
You gave me a tip with this chain feature.
I changed a few lines of your code, and it worked as I wanted:
import std.stdio;
import std.range;
import std.array;
void main()
{
int[] arr = [0,1,2,3,4,5,6,7,8,9];
immutable position = arr.length / 2;
immutable newValue = 42;
auto r = chain(arr[0 .. position], [ newValue ], arr[position
.. $-1]);
arr = array(r);
foreach(int i; arr)
writefln(%d, i);
}
Thanks,
Matheus.
Re: Arrays - Inserting and moving data
On 02/09/2012 11:03 AM, H. S. Teoh wrote:
On Thu, Feb 09, 2012 at 10:30:22AM -0800, Ali Çehreli wrote:
[...]
But if you don't actually want to modify the data, you can merely
access the elements in-place by std.range.chain:
import std.stdio;
import std.range;
void main()
{
int[] arr = [0,1,2,3,4,5,6,7,8,9];
immutable position = arr.length / 2;
immutable newValue = 42;
auto r = chain(arr[0 .. position], [ newValue ], arr[position +
1 .. $]);
writeln(r);
}
'r' above is a lazy range that just provides access to the three
ranges given to it. 'arr' does not change in any way.
[...]
Wow! This is really cool. So you *can* have O(1) insertions in the
middle of an array after all. :)
Of course, you probably want to flatten it once in a while to keep
random access cost from skyrocketing.
O(1) would be violated only if there are too many actual ranges.
(I'm assuming delegates or
something equivalent are involved in generating the lazy range?)
Simpler than that. :) The trick is that chain() returns a range object
that operates lazily. I have used chain() as an example for finite
RandomAccessRange types (I used the name 'Together' instead of Chain).
Search for Finite RandomAccessRange here:
http://ddili.org/ders/d.en/ranges.html
And yes, I note there that the implementation is not O(1). Also look
under the title Laziness in that chapter.
Ali
Re: Arrays - Inserting and moving data
On Thursday, 9 February 2012 at 19:49:43 UTC, Timon Gehr wrote: Note that this code does the same, but is more efficient if you don't actually need the array: Yes I know, In fact I need re-think the way I code with this new features of D, like ranges for example. Thanks, Matheus.
