D - Array slicing Associative and Rectangular arrays?
- Russ Lewis (18/18) Feb 18 2002 * Can you array slice associative arrays? IMHO, this is an almost
- Pavel Minayev (10/23) Feb 18 2002 How exactly do you slice an associative array? With item indices?
- Russ Lewis (24/48) Feb 18 2002 This is kind of what I'm thinking about:
- Pavel Minayev (8/15) Feb 18 2002 that
- Walter (6/10) Feb 20 2002 Correct, there is not a defined order to the values, and they are not
- Pavel Minayev (6/10) Feb 20 2002 I'd still request some form of loop to scan through the entire
- Russell Borogove (3/17) Feb 20 2002 Seconded.
- Russ Lewis (8/18) Feb 21 2002 Is the result of strcmp() defined or implementation dependent? If the
- Pavel Minayev (10/12) Feb 21 2002 Don't forget that D associative arrays don't necessary have string
- Russ Lewis (14/26) Feb 21 2002 Great! But I didn't know that...and I don't see it in the online docs. ...
- Pavel Minayev (11/15) Feb 21 2002 The
- Karl Bochert (6/8) Feb 21 2002 Is that the second through fourth elements of start?
- Pavel Minayev (5/12) Feb 21 2002 Second through fourth (counting from 1).
* Can you array slice associative arrays? IMHO, this is an almost
must-have feature...but be careful, Pavel (playful grin), because it
won't look right to have end-exclusive syntax here, either
* What happens if you array slice a rectangular array and try to set it
"by reference" to another array?
int[5][5] start = ....;
int[3][3] copyByValue,copyByReference;
copyByValue[] = start[1..4][1..4]; // doesn't seem like too much
trouble,
// copies the
values over
copyByReference = start[1..4][1..4]; // how in the world do you
do this?
--
The Villagers are Online! villagersonline.com
.[ (the fox.(quick,brown)) jumped.over(the dog.lazy) ]
.[ (a version.of(English).(precise.more)) is(possible) ]
?[ you want.to(help(develop(it))) ]
Feb 18 2002
"Russ Lewis" <spamhole-2001-07-16 deming-os.org> wrote in message news:3C711ADA.15D57A6C deming-os.org...* Can you array slice associative arrays? IMHO, this is an almost must-have feature...but be careful, Pavel (playful grin), because it won't look right to have end-exclusive syntax here, eitherHow exactly do you slice an associative array? With item indices? Then the same rules would apply as for normal arrays, including end-exclusive syntax...* What happens if you array slice a rectangular array and try to set it "by reference" to another array? int[5][5] start = ....; int[3][3] copyByValue,copyByReference; copyByValue[] = start[1..4][1..4]; // doesn't seem like too much trouble, // copies the values over copyByReference = start[1..4][1..4]; // how in the world do you do this?I believe there's no such thing as "rectangular slice" in D. start[1..4] is an array of 3 elements of type int[5]. Now you slice it once again with [1..4] and get an out-of-range exception because there's no element with index 3. You could, however, slice it as start[1..4][1..3], which is absolutely the same as start[2..3].
Feb 18 2002
Pavel Minayev wrote:"Russ Lewis" <spamhole-2001-07-16 deming-os.org> wrote in message news:3C711ADA.15D57A6C deming-os.org...This is kind of what I'm thinking about: class Book {...}; Book[] booksOnShelf; ... Book[] booksToCheckOut = booksOnShelf["Anne of Green Gables" .. "Farenheit 451"]; You see, I'm trying a slice here to include the range of books, assuming that this associative array was indexed by title. I think this feature would be very useful for people using associative arrays. But presumably, I want to make sure that I get my copy of "Farenheit 451" (but nothing after it). How do I do that? You can't really do +1 to string. Of course, I could include up to "G" and then cut the extras off of the tail, but then the usefulness of slicing is greatly diminished. Today, my record on questions relating to arrays is about 0-2, so maybe there's some easy way to do this that I've missed (smirk)* Can you array slice associative arrays? IMHO, this is an almost must-have feature...but be careful, Pavel (playful grin), because it won't look right to have end-exclusive syntax here, eitherHow exactly do you slice an associative array? With item indices? Then the same rules would apply as for normal arrays, including end-exclusive syntax...d'oh! You're right, of course. The "array slicing operator" returns an array with as many dimensions as it started with...so rectangular slicing isn't even an issue. Do it with a for loop :p -- The Villagers are Online! villagersonline.com .[ (the fox.(quick,brown)) jumped.over(the dog.lazy) ] .[ (a version.of(English).(precise.more)) is(possible) ] ?[ you want.to(help(develop(it))) ]* What happens if you array slice a rectangular array and try to set it "by reference" to another array? int[5][5] start = ....; int[3][3] copyByValue,copyByReference; copyByValue[] = start[1..4][1..4]; // doesn't seem like too much trouble, // copies the values over copyByReference = start[1..4][1..4]; // how in the world do you do this?I believe there's no such thing as "rectangular slice" in D. start[1..4] is an array of 3 elements of type int[5]. Now you slice it once again with [1..4] and get an out-of-range exception because there's no element with index 3. You could, however, slice it as start[1..4][1..3], which is absolutely the same as start[2..3].
Feb 18 2002
"Russ Lewis" <spamhole-2001-07-16 deming-os.org> wrote in message news:3C713B38.3099017D deming-os.org...Book[] booksOnShelf; ... Book[] booksToCheckOut = booksOnShelf["Anne of Green Gables" .. "Farenheit 451"]; You see, I'm trying a slice here to include the range of books, assumingthatthis associative array was indexed by title. I think this feature wouldbevery useful for people using associative arrays.The key word here is "indexed". I'm not sure that D associative arrays are indexed - in fact, I'm not sure that there's _any_ strictly defined order of keys. As Walter has said before, the exact implementation of associative array is left to the concrete compiler.
Feb 18 2002
"Pavel Minayev" <evilone omen.ru> wrote in message news:a4rij2$26n8$1 digitaldaemon.com...The key word here is "indexed". I'm not sure that D associative arrays are indexed - in fact, I'm not sure that there's _any_ strictly defined order of keys. As Walter has said before, the exact implementation of associative array is left to the concrete compiler.Correct, there is not a defined order to the values, and they are not "indexed" in the sense of looping through the members of an array by an index. The way to enumerate all the members is by converting the associative array to a dynamic array.
Feb 20 2002
"Walter" <walter digitalmars.com> wrote in message news:a4vpei$ng8$2 digitaldaemon.com...Correct, there is not a defined order to the values, and they are not "indexed" in the sense of looping through the members of an array by an index. The way to enumerate all the members is by converting the associative array to a dynamic array.I'd still request some form of loop to scan through the entire associative array without converting it to dynamic key/value arrays. Let the order be "implementation-defined", there are many situations where it just doesn't matter.
Feb 20 2002
Russell Borogove <kaleja estarcion.com> Pavel Minayev wrote:"Walter" <walter digitalmars.com> wrote in message news:a4vpei$ng8$2 digitaldaemon.com...Seconded. -RBCorrect, there is not a defined order to the values, and they are not "indexed" in the sense of looping through the members of an array by an index. The way to enumerate all the members is by converting the associative array to a dynamic array.I'd still request some form of loop to scan through the entire associative array without converting it to dynamic key/value arrays. Let the order be "implementation-defined", there are many situations where it just doesn't matter.
Feb 20 2002
Pavel Minayev wrote:"Walter" <walter digitalmars.com> wrote in message news:a4vpei$ng8$2 digitaldaemon.com...Is the result of strcmp() defined or implementation dependent? If the former, then strcmp()'s comparison algorithm would work fine for me.... -- The Villagers are Online! villagersonline.com .[ (the fox.(quick,brown)) jumped.over(the dog.lazy) ] .[ (a version.of(English).(precise.more)) is(possible) ] ?[ you want.to(help(develop(it))) ]Correct, there is not a defined order to the values, and they are not "indexed" in the sense of looping through the members of an array by an index. The way to enumerate all the members is by converting the associative array to a dynamic array.I'd still request some form of loop to scan through the entire associative array without converting it to dynamic key/value arrays. Let the order be "implementation-defined", there are many situations where it just doesn't matter.
Feb 21 2002
"Russ Lewis" <spamhole-2001-07-16 deming-os.org> wrote in message news:3C75179F.EF2FE1BF deming-os.org...Is the result of strcmp() defined or implementation dependent? If the former, then strcmp()'s comparison algorithm would work fine for me....Don't forget that D associative arrays don't necessary have string keys. It's perfectly valid to have an int, float, or even Object as a key. Also, any "comparison algorithm" sorta limits the implementation - it either has to store the keys in that order in memory, or the iteration process will be quite slow (because a look-up is performed for each key in the table). How do you implement an ordered scan for a hash table, for example?
Feb 21 2002
Pavel Minayev wrote:"Russ Lewis" <spamhole-2001-07-16 deming-os.org> wrote in message news:3C75179F.EF2FE1BF deming-os.org...Great! But I didn't know that...and I don't see it in the online docs. The closest I see is a statement that "Associated arrays are supported for all following types", which is hard to understand, but I guessed meant "you can have an associative array (keyed by strings) of any type".Is the result of strcmp() defined or implementation dependent? If the former, then strcmp()'s comparison algorithm would work fine for me....Don't forget that D associative arrays don't necessary have string keys. It's perfectly valid to have an int, float, or even Object as a key.Also, any "comparison algorithm" sorta limits the implementation - it either has to store the keys in that order in memory, or the iteration process will be quite slow (because a look-up is performed for each key in the table). How do you implement an ordered scan for a hash table, for example?Right. It would be nice to be able to slice these arrays with compiler support in the language. I don't really care the underlying algorithm; I was just hoping that I could have access to the easy functionality. However if more than strings are supported, then it gets hard. -- The Villagers are Online! villagersonline.com .[ (the fox.(quick,brown)) jumped.over(the dog.lazy) ] .[ (a version.of(English).(precise.more)) is(possible) ] ?[ you want.to(help(develop(it))) ]
Feb 21 2002
"Russ Lewis" <spamhole-2001-07-16 deming-os.org> wrote in message news:3C753CF5.D4313464 deming-os.org...Great! But I didn't know that...and I don't see it in the online docs.Theclosest I see is a statement that "Associated arrays are supported for all following types", which is hard to understand, but I guessed meant "youcanhave an associative array (keyed by strings) of any type".Just remember the syntax: int[char[]] foo; // keys are char[] char[][double] bar; // keys are double Object[Object] baz; // keys are Object The only thing is that currently DMD alpha only supports int[char[]] =) I guess this also includes pointers since they're 32-bit as well (or am I wrong, Walter?).
Feb 21 2002
I believe there's no such thing as "rectangular slice" in D. start[1..4] is an array of 3 elements of type int[5].Is that the second through fourth elements of start? Or the first through third? Neither seems to be what [1..4] is saying! [1..4] clearly shows either a 1 and a 4 or a 'first' and a 'fourth' inside the brackets (array). Karl Bochert
Feb 21 2002
"Karl Bochert" <kbochert ix.netcom.com> wrote in message news:1105_1014316952 bose...Second through fourth (counting from 1).I believe there's no such thing as "rectangular slice" in D. start[1..4] is an array of 3 elements of type int[5].Is that the second through fourth elements of start? Or the first through third?Neither seems to be what [1..4] is saying! [1..4] clearly shows either a 1 and a 4 or a 'first' and a 'fourth' inside the brackets (array).C (and D) arrays are zero-based, you know =) So the element isn't actually 'first', but 'zeroth'.
Feb 21 2002