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Re: a newbie question on code efficiency [message #26294 is a reply to message #26293] Sat, 18 August 2001 05:44 Go to previous messageGo to previous message
Dominic R. Scales is currently offline  Dominic R. Scales
Messages: 12
Registered: April 2001
Junior Member
David Fanning wrote:

> Uh, I think you must have tried this:
>
> e = b > cutoff
>
> I can assure you that this:
>
> e = b GT cutoff
>
> gives you a mask of 0s and 1s. :-)
>
> Cheers,
>
> David
>
Hi David,

this seems to be not true as b = a > cutoff sets the values smaller
than cutoff to cutoff and keeps the others as they are.

IDL> a=bindgen(10,10)
IDL> b = a > 50
IDL> print,a
0 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26 27 28 29
30 31 32 33 34 35 36 37 38 39
40 41 42 43 44 45 46 47 48 49
50 51 52 53 54 55 56 57 58 59
60 61 62 63 64 65 66 67 68 69
70 71 72 73 74 75 76 77 78 79
80 81 82 83 84 85 86 87 88 89
90 91 92 93 94 95 96 97 98 99
IDL> b= a > 50
IDL> print,b
50 50 50 50 50 50 50 50 50 50
50 50 50 50 50 50 50 50 50 50
50 50 50 50 50 50 50 50 50 50
50 50 50 50 50 50 50 50 50 50
50 50 50 50 50 50 50 50 50 50
50 51 52 53 54 55 56 57 58 59
60 61 62 63 64 65 66 67 68 69
70 71 72 73 74 75 76 77 78 79
80 81 82 83 84 85 86 87 88 89
90 91 92 93 94 95 96 97 98 99
IDL>

the following does the trick:

IDL> b[where(a le 50)] = 0
IDL> b[where(a gt 50)] = 1
IDL> print,b
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1
IDL>


--
Dipl. Phys. Dominic R. Scales | Aero-Sensing Radarsysteme GmbH
Tel: +49 (0)8153-90 88 90 | c/o DLR Oberpfaffenhofen
Fax: +49 (0)8153-908 700 | 82234 Wessling, Germany
WWW: aerosensing.de | email: Dominic.Scales@aerosensing.de

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