Array Comparison in Fortran 90/95

September 11, 2008, 10:50

Hi FORTRAN 90/95 Users: Want to know some efficient way of comparing two or more large size arrays in FORTRAN 90/95. Thanks

September 11, 2008, 11:10

To be a little more specific: The arrays could be of different lengths and want to compare them for duplication. -Malik

September 11, 2008, 12:55

Oh, they are integer arrays representing sets? You want to determine what integers appear in both arrays? If the range of possible values is known and reasonable, you can mask a bit-array. Otherwise, just sort the arrays.

September 11, 2008, 13:41

Thanks Jed. Yes, I have integer arrays. The range is not known all the time. Comparison by sorting turns out to be very time consuming. Some other suggestion, please!

September 11, 2008, 14:14

Keep the arrays sorted or partially sorted. If you don't sort, you end up with O(n^2) which is much worse. A radix sort shouldn't be that bad. Where do these arrays come from? How big are they? I assume you solve equations at some point? Or is this for mesh manipulation? Would a different data structure be better?

September 11, 2008, 10:50	Array Comparison in Fortran 90/95	#1
M Malik Guest Posts: n/a	Hi FORTRAN 90/95 Users: Want to know some efficient way of comparing two or more large size arrays in FORTRAN 90/95. Thanks

September 11, 2008, 11:10	Re: Array Comparison in Fortran 90/95	#2
M Malik Guest Posts: n/a	To be a little more specific: The arrays could be of different lengths and want to compare them for duplication. -Malik

September 11, 2008, 12:55	Re: Array Comparison in Fortran 90/95	#3
Jed Guest Posts: n/a	Oh, they are integer arrays representing sets? You want to determine what integers appear in both arrays? If the range of possible values is known and reasonable, you can mask a bit-array. Otherwise, just sort the arrays.

September 11, 2008, 13:41	Re: Array Comparison in Fortran 90/95	#4
M Malik Guest Posts: n/a	Thanks Jed. Yes, I have integer arrays. The range is not known all the time. Comparison by sorting turns out to be very time consuming. Some other suggestion, please!

September 11, 2008, 14:14	Re: Array Comparison in Fortran 90/95	#5
Jed Guest Posts: n/a	Keep the arrays sorted or partially sorted. If you don't sort, you end up with O(n^2) which is much worse. A radix sort shouldn't be that bad. Where do these arrays come from? How big are they? I assume you solve equations at some point? Or is this for mesh manipulation? Would a different data structure be better?

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