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.NET Forum / Languages / C# / February 2008Should i use Array, double[][] or double[,]?
I'm designing a class that will base its functionality on one (or more) arrays of doubles. Each array will be of the same length pairwise but their number may vary from a single one up to several. The usual way i'd use in C++ would be to declare the following. double[][] *data; In C# i have two more options. Given that the number of arrays might vary as the program goes on (as in: i'd like to remove and add arrays on the fly), i wonder if there's a gain in deploying Array class directly. Also, which would be more prefered in C# - the jagged or the multidimensional array? -- Regards Konrad Viltersten -------------------------------- sleep - a substitute for coffee for the poor ambition - lack of sense to be lazy > I'm designing a class that will base its > functionality on one (or more) arrays of > doubles. Each array will be of the same > length pairwise but their number may vary from a single one up to > several. What does "will be of the same length pairwise" mean? Pairwise to what? Each other? Something else? Do you just mean that every double[] will be exactly the same length? > The usual way i'd use in C++ would be to > declare the following. > double[][] *data; Granted, it's been awhile since I've done a lot of C++ coding. It seems that every year that goes by, I forget at least one other important part of the language. But my recollection is that a declaration like that is quite a bit different from what you've described so far (the above describes a two-dimensional array of pointers to doubles, not just to doubles), and isn't allowed unless you provide the exact dimensions of the array in the declaration (either in the variable declaration itself or an initializer). > In C# i have two more options. Given that the number of arrays might > vary as [quoted text clipped - 5 lines] > C# - the jagged or the multidimensional > array? From your description, possibly neither. In particular, you wrote: "i'd like to remove and add arrays on the fly". If by this you mean that you'd add or remove single-dimensional arrays from the array of arrays, then it seems that using a dynamic collection of arrays would be better. For example, List<double[]>. If you simply mean that you'd add and remove these jagged/multi-dimensional arrays dynamically to and from some other collection, then it really just comes down to what represents the data the best. The multi-dimensional array works best for situations when you really are using all of the elements. A jagged array works best if the second dimension referenced by the first can vary in size according to the second. Which shouldn't be surprising, since those statements are not far from describing precisely what the multi-dimensional array and jagged array are. :) Pete >> I'm designing a class that will base its functionality >> on one (or more) arrays of doubles. Each array will [quoted text clipped - 3 lines] > What does "will be of the same length pairwise" mean? > Pairwise to what? Each other? Yes. As in - for any pair of the elements you pick, the length will be equal. I thought it was a common expression... Too much math, i guess... >> The usual way i'd use in C++ would be to >> declare the following. >> double[][] *data; > > But my recollection is that a declaration like that is quite > a bit different from what you've described so far... It might. The message got through and that's good enough for me at this point. > In particular, you wrote: "i'd like to remove and add arrays > on the fly". ...[it] seems that using a dynamic collection of > arrays would be better. For example, List<double[]>. Thanks, that's what i was looking for! -- Regards Konrad Viltersten -------------------------------- sleep - a substitute for coffee for the poor ambition - lack of sense to be lazy Konrad, Personally, I would use a List<double[]>. You could treat it as a multi-dimensional array or a jagged array (since every element in the list doesn't have to be the same length), and you don't have to worry about re-copying the array as the number of arrays grows.  Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com > I'm designing a class that will base its > functionality on one (or more) arrays of [quoted text clipped - 21 lines] > sleep - a substitute for coffee for the poor > ambition - lack of sense to be lazy > Konrad, > > Personally, I would use a List<double[]>. You could treat it as a > multi-dimensional array or a jagged array (since every element in the list > doesn't have to be the same length), and you don't have to worry about > re-copying the array as the number of arrays grows. The other option is List<List<double>> Michael >> Personally, I would use a List<double[]>. > > The other option is List<List<double>> Acutally, in my case, the first way is most appropriate because the lengths of the inner arrays will never change, only their number (if that!). Thanks anyway. -- Regards Konrad Viltersten -------------------------------- sleep - a substitute for coffee for the poor ambition - lack of sense to be lazy > Acutally, in my case, the first way is most > appropriate because the lengths of the inner arrays will never change, > only their > number (if that!). Yep, this method is only useful if the arrays can change in size. > Thanks anyway. > [quoted text clipped - 4 lines] > sleep - a substitute for coffee for the poor > ambition - lack of sense to be lazy >> I'm designing a class that will base its >> functionality on one (or more) arrays of [quoted text clipped - 9 lines] > worry about re-copying the array as the > number of arrays grows. Yes, that's along the other replies as well so i see no problem using it. (I'm sure Peter D. will gladly point out at least one ust to create a pathological example. The occasion is on me!) -- Regards Konrad Viltersten -------------------------------- sleep - a substitute for coffee for the poor ambition - lack of sense to be lazy > The usual way i'd use in C++ would be to > declare the following. > double[][] *data; I don't think so. It is not valid C++ syntax. > In C# i have two more options. Given that the number of arrays might > vary as > the program goes on (as in: i'd like to > remove and add arrays on the fly), i wonder if there's a gain in > deploying Array class directly. The Array class is the base class for arrays - it is not a different type of arrays. > Also, which would be more prefered in > C# - the jagged or the multidimensional > array? square data => multi dim non square data => jagged Arne >> The usual way i'd use in C++ would be to >> declare the following. >> double[][] *data; > > I don't think so. It is not valid C++ syntax. Allright, already, so i made an a.s by giving "sort-of" code. Big deal! It's not like a compiler would misunderstand ones intentions! Oh, wait. It would... :) -- Regards Konrad Viltersten -------------------------------- sleep - a substitute for coffee for the poor ambition - lack of sense to be lazy >>> The usual way i'd use in C++ would be to >>> declare the following. [quoted text clipped - 5 lines] > giving "sort-of" code. Big deal! It's not like a compiler would > misunderstand ones intentions! Oh, wait. It would... :) Compilers are known to be rather picky. :-) I still remember the Fortran compiler 25 years ago that would not compile a program because it had an empty line at the bottom .... Arne > I still remember the Fortran compiler 25 years ago > that would not compile a program because it had an > empty line at the bottom .... I still use an 8051 compiler than won't compile unless you have an empty line. Michael >> I still remember the Fortran compiler 25 years ago >> that would not compile a program because it had an >> empty line at the bottom .... > > I still use an 8051 compiler than won't compile unless you have an > empty line. Assuming you mean C here -- preprocessor directives are required to end in a newline, not end of file So if the last line is #endif, then yes that's expected. If the last line was for example }, then I believe that's a nonconformant compiler > Michael > Assuming you mean C here -- > [quoted text clipped - 4 lines] > If the last line was for example }, then I believe that's a nonconformant > compiler This is a free assembly language compiler. I can't remember the name of it or who wrote it as it's been a few months since I've used it. Michael Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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