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Re: Finding Common Elements in Two Arrays [message #2190 is a reply to message #2111]

Fri, 03 June 1994 06:02

landers
Messages: 45
Registered: May 1993

Member

I'm gonna rebut my own post.... a bit.

In article <1994Jun2.223011.12904@mksol.dseg.ti.com>, landers@tsunami.dseg.ti.com (David Landers) writes:

|> This is the first thing that poped into my head...
|>
|> Make 2-D arrays of A and B, like this:
|>
|> AA = A(*) # REPLICATE(1, N_ELEMENTS(B))
|> BB = REPLICATE(1, N_ELEMENTS(A)) # B(*)
|>

May be better to do:

Na = N_ELEMENTS(a)
Nb = N_ELEMENTS(b)
L = LINDGEN(Na,Nb)
AA = A( L MOD Na )
BB = B( L / Na )

|> Now you can compare all combinations of one to the other:
|>
|> ALIKE = UNIQUE( AA( WHERE( AA EQ BB ) ) )
|>
|> Then ALIKE contains a sorted list of the elements common to both arrays.

Yep. The advantage to the above over the matrix multiply (#) method is that
it may be faster, and it will work with strings and structures (although EQ
doesn't work with structs).

|> This could be more efficient, since you really only need a triangular array to
|> do this (you get 2 of each match, hence the UNIQUE).

What did I say? This is total nonsense (the triangular array bit). Just
ignore this.

|>
|> --
|> Dave

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[Message index]

		Finding Common Elements in Two Arrays By: kucera on Wed, 01 June 1994 13:45
		Re: Finding Common Elements in Two Arrays By: stl on Wed, 01 June 1994 23:26
		Re: Finding Common Elements in Two Arrays By: stl on Mon, 06 June 1994 01:09
		Re: Finding Common Elements in Two Arrays By: landers on Fri, 03 June 1994 06:10
		Re: Finding Common Elements in Two Arrays By: landers on Fri, 03 June 1994 06:02
		Re: Finding Common Elements in Two Arrays By: dan on Wed, 01 June 1994 16:23
		Re: Finding common elements in two arrays By: andy on Tue, 26 July 1994 09:39

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