Numeric: 'where' function conditions

[Jorl Shefner]

Could anyone tell me the efficient way to do this? Extracting values
from an array for a single condition (say all values greater than 'x')
using 'where' and 'compress' is simple enough.
[color=blue][color=green][color=darkred]
>>> from Numeric import arange,where,co mpress
>>> data= arange(10)
>>> data= [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> mask= where((data > 3),1,0)
>>> result= compress(mask,d ata)
>>> result[/color][/color][/color]
array([4, 5, 6, 7, 8, 9])

But, 'where' doesn't appear to allow for multiple conditions in one
statement. For instance, I'd like to do something like:

mask= where((3 < data <= 7),1,0)

but, this won't work.

So, the best I could come up with was this more complicated process that
requires 2 separate masks and an extra temporary array.
[color=blue][color=green][color=darkred]
>>> mask1= where((data > 3),data,0)
>>> mask1[/color][/color][/color]
array([0, 0, 0, 0, 4, 5, 6, 7, 8, 9])[color=blue][color=green][color=darkred]
>>> mask2= where((mask1<= 7),mask1,0)
>>> mask2[/color][/color][/color]
array([0, 0, 0, 0, 4, 5, 6, 7, 0, 0])[color=blue][color=green][color=darkred]
>>> r= compress(mask2, data)
>>> r[/color][/color][/color]
array([4, 5, 6, 7])

Is there a more concise way?

Thanks,

J.S.

[Robert Kern]

Re: Numeric: 'where' function conditions

Jorl Shefner wrote:[color=blue]
> Could anyone tell me the efficient way to do this? Extracting values
> from an array for a single condition (say all values greater than 'x')
> using 'where' and 'compress' is simple enough.
>
>[color=green][color=darkred]
>>>>from Numeric import arange,where,co mpress
>>>>data= arange(10)
>>>>data= [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>>>mask= where((data > 3),1,0)
>>>>result= compress(mask,d ata)
>>>>result[/color][/color]
>
> array([4, 5, 6, 7, 8, 9])
>
> But, 'where' doesn't appear to allow for multiple conditions in one
> statement. For instance, I'd like to do something like:
>
> mask= where((3 < data <= 7),1,0)
>
> but, this won't work.[/color]

Right. "3 < data" creates an array of 0s and 1s where the condition is
false and true, respectively. You don't need where() at all.

Try

mask = logical_and(3 < data, data <= 7)

--
Robert Kern
rkern@ucsd.edu

"In the fields of hell where the grass grows high
Are the graves of dreams allowed to die."
-- Richard Harter

[Jorl Shefner]

Re: Numeric: 'where' function conditions

In article <cogan6$kt0$1@n ews1.ucsd.edu>, Robert Kern <rkern@ucsd.edu >
wrote:
[color=blue]
>
> Right. "3 < data" creates an array of 0s and 1s where the condition is
> false and true, respectively. You don't need where() at all.
>
> Try
>
> mask = logical_and(3 < data, data <= 7)[/color]

Great. That's exactly what I needed. Thanks.