where function

[vorticitywolfe]

Is there a function in Python analogous to the "where" function in
IDL?

x=[0,1,2,3,4,2,8,9]
print where(x=2)

output:
[2,5]

[bearophileHUGS]

vorticitywo:

Is there a function in Python analogous to the "where" function in
IDL?

Python gives very elastic syntax, you can simply do:

data = [0,1,2,3,4,2,8,9]
print [pos for pos, el in enumerate(data) if el==2]

Bye,
bearophile

[drochom]

On 18 Mar, 15:19, [e-mail] wrote:

Is there a function in Python analogous to the "where" function in
IDL?

x=[0,1,2,3,4,2,8,9]
print where(x=2)

output:
[2,5]

You can try this:

print filter( lambda x: a[x]==2, range(len(a)))

However it's not the best solution...

[vorticitywolfe]

On Mar 18, 10:48 pm, [e-mail] wrote:

vorticitywo:

Is there a function in Python analogous to the "where" function in
IDL?

Python gives very elastic syntax, you can simply do:

data = [0,1,2,3,4,2,8,9]
print [pos for pos, el in enumerate(data) if el==2]

Bye,
bearophile

Thank you both, a little more cumbersome than I expected, but it does
the job! Thanks!

[Shane Geiger]

a =
[0,1,2,3,4,2,8,9]

# method
1

print [i for i in xrange(len(a)) if
a[i]==2]

def
where(a,val):

return [i for i in xrange(len(a)) if
a[i]==val]

# method
2

print
where(a,2)



vo************@gmail.com wrote:

On Mar 18, 10:48 pm, [e-mail] wrote:

>vorticitywo:

>>Is there a function in Python analogous to the "where" function in
IDL?

Python gives very elastic syntax, you can simply do:

data = [0,1,2,3,4,2,8,9]
print [pos for pos, el in enumerate(data) if el==2]

Bye,
bearophile

Thank you both, a little more cumbersome than I expected, but it does
the job! Thanks!

--
Shane Geiger
IT Director
National Council on Economic Education
sg*****@ncee.net | 402-438-8958 | http://www.ncee.net

Leading the Campaign for Economic and Financial Literacy

[Steven Bethard]

vo************@gmail.com wrote:

Is there a function in Python analogous to the "where" function in
IDL?

x=[0,1,2,3,4,2,8,9]
print where(x=2)

output:
[2,5]

If you're doing a lot of this kind of thing, you probably want to use
numpy::

>>import numpy
x = numpy.array([0, 1, 2, 3, 4, 2, 8, 9])
numpy.where(x == 2)

(array([2, 5]),)

You can find numpy here:

http://numpy.scipy.org/

STeVe

[Scott David Daniels]

vo************@gmail.com wrote:

On Mar 18, 10:48 pm, [e-mail] wrote:

>[...fine solutions to the problem as asked...]

Thank you both, a little more cumbersome than I expected, but it does
the job! Thanks!

The obvious simple near-equivalent is:

data = range(33,99)
print data.index(45)

And "generalized":
data = [x % 9 for x in range(30)]
result = []
former = -1
try:
while True:
former = data.index(3, former + 1)
result.append(former)
except ValueError:
print result
else:
print 'Nothing found'

--
--Scott David Daniels
sc***********@acm.org