| array [message #90543] |
Mon, 09 March 2015 02:27  |
8sushil
Messages: 2
Registered: March 2015
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Junior Member |
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how can i print the location in the matrix knowing the value in that location.
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| Re: array [message #90544 is a reply to message #90543] |
Mon, 09 March 2015 02:50  |
Helder Marchetto
Messages: 520
Registered: November 2011
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Senior Member |
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On Monday, March 9, 2015 at 10:27:39 AM UTC+1, 8sushil wrote:
> how can i print the location in the matrix knowing the value in that location.
User the where() function as described here:
http://exelisvis.com/docs/WHERE.html
The result is a 1D location. If your matrix/array is 2D and you *need* a 2D result, then you can use array_indices():
http://exelisvis.com/docs/ARRAY_INDICES.html
If the value you're looking for is myValue and the matrix/array is myArray, then you can use this:
position = where(myValue eq myArray, cnt)
print, 'my 1D position is: ', position
print, 'my 2D position is: ', array_indices(myArray, position)
Make sure you check how to use the cnt result (-1 if not found!). This should get you going. If you're looking for floats, it can be a bit more tricky.
Cheers,
Helder
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| Re: array [message #90548 is a reply to message #90546] |
Mon, 09 March 2015 12:47 |
Jeremy Bailin
Messages: 618
Registered: April 2008
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Senior Member |
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> Since you're the Value_locate guy, can it be used with 2d arrays? If so, how is monotonic defined in these cases? By using 1d indexes for a 2d array?
Yes, exactly -- it needs to be monotonic with respect to 1D indices.
> And in case of a 2d array, when does one end up with a monotonic 2d array (however this is defined)?
For example:
q = indgen(N1, N2)
gives you an array that is monotonic as far as Value_Locate is concerned. Also, I will sometimes create a 2D array that is monotonic by stacking together individually-monotonic 1D arrays with offsets in the second dimension for the express purpose of using Value_Locate on it. For example, if W is an N1 x N2 array where each W[*,i] is sorted, then you can create a monotonic 2D array is follows:
; in order to make the array monotonic, we need to add an offset to
; each row that will ensure that the minimum value for every subsequent
; row is pushed to being greater than the maximum value of each previous
; row. The following example will technically only work for non-negative W
; and for either integers or not-too-large floats, but can be generalized.
offset = max(W)+1
Wdimen = size(W, /dimen)
; create an N1 x N2 array that adds an appropriate increment to each row
W2 = W + rebin(offset * lindgen(1, Wdimen[1]), Wdimen, /sample)
-Jeremy.
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