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Re: how to get the index of the maximum element in each row for a 2D matrix efficiently [message #36300 is a reply to message #36295]

Fri, 29 August 2003 12:05

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Fri, 29 Aug 2003 10:34:52 -0700, Xiaoying Jin wrote:

> Hi, there,
>
> Suppose we have a 2D dimension matrix A(i,j), I want to get the index of
> the max element in each row.
>
> Basicly, we can do a for loop on each row, then use 'max' function to
> get the index for each row. But for a matrix having many rows, that will
> be pretty slow-->not efficient. Is there a function that can return what
> I want if I input a 2D matrix.
>
> In the previous version, 'total' function can only get the total values
> of the whole matrix. Now it can get the total values on each dimension
> by setting the keyword 'dimension'.
>
> So how is 'max' working?

Starting with v5.6, MAX will do this for you with its own DIMENSION
keyword. Remember that in IDL dimensions start, perversely, with 1,
as opposed to everything else, which is 0 based. As of now we can
thread the following:

TOTAL
PRODUCT
MIN
MAX
MEDIAN

The only remaining operators I wish could be dimensionally threaded in
this way are AND, OR, and especially the new && and ||
short-circuiting ops.

JD

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[Message index]

		Re: how to get the index of the maximum element in each row for a 2D matrix efficiently By: JD Smith on Tue, 02 September 2003 10:12
		Re: how to get the index of the maximum element in each row for a 2D matrix efficiently By: henrygroe on Sat, 30 August 2003 13:33
		Re: how to get the index of the maximum element in each row for a 2D matrix efficiently By: the_cacc on Fri, 29 August 2003 17:33
		Re: how to get the index of the maximum element in each row for a 2D matrix efficiently By: xje4e on Fri, 29 August 2003 15:23
		Re: how to get the index of the maximum element in each row for a 2D matrix efficiently By: JD Smith on Fri, 29 August 2003 12:05

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