FAQ
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.
from Numeric import arange,where,compress
data= arange(10)
data= [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
mask= where((data > 3),1,0)
result
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.
mask1= where((data > 3),data,0)
array([0, 0, 0, 0, 4, 5, 6, 7, 8, 9])
array([0, 0, 0, 0, 4, 5, 6, 7, 0, 0])
r
array([4, 5, 6, 7])

Is there a more concise way?

Thanks,

J.S.

## Search Discussions

•  at Nov 29, 2004 at 11:17 pm ⇧

Jorl Shefner wrote:
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.

from Numeric import arange,where,compress
data= arange(10)
data= [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
mask= where((data > 3),1,0)
result
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.
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 at ucsd.edu

"In the fields of hell where the grass grows high
Are the graves of dreams allowed to die."
-- Richard Harter
•  at Nov 30, 2004 at 2:48 pm ⇧

In article <cogan6\$kt0\$1 at news1.ucsd.edu>, Robert Kern wrote:
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)
Great. That's exactly what I needed. Thanks.

## Related Discussions

 view thread | post
Discussion Overview
 group python-list categories python posted Nov 29, '04 at 11:05p active Nov 30, '04 at 2:48p posts 3 users 2 website python.org

### 2 users in discussion

Content

People

Support

Translate

site design / logo © 2022 Grokbase