Get a value in a numpy array from a index in a variable

Question

I am trying to access a value in a multi dimensional numpy array. This can be easily done when you know everything, for exemple :

T = numpy.arrange(9).reshape(3, 3) T[2, 2]

And it returns 8, which is what I want. Now, Let's assume [2, 2] is stored in index variable. How can I do to take the value in T with the index stored in index ? I would like to do T[index] but it returns the last row twice (pretty logical but not what I want).

Thank you !

Try ind=tuple(2,2); x[ind]

hpaulj
– hpaulj

2016-02-08 15:25:50 +00:00
Commented Feb 8, 2016 at 15:25 — hpaulj
– hpaulj, Commented Feb 8, 2016 at 15:25
Thanks, works perfectly !

clementescolano
– clementescolano

2016-02-08 15:29:09 +00:00
Commented Feb 8, 2016 at 15:29 — clementescolano
– clementescolano, Commented Feb 8, 2016 at 15:29

hpaulj · Accepted Answer · 2016-02-08 16:48:21Z

2

Try

ind=tuple(2,2)
x[ind]

x[2,2] is the same as x[(2,2)] which is translated into a method call: x.__getitem__((2,2)).

Some numpy functions build an index as a list or array, then convert it to a tuple for use in the index.

answered Feb 8, 2016 at 16:48

hpaulj

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1 Comment

pas-calc Over a year ago

If you want to access multiple values at once, make sure to use a 2-tuple which consists of two arrays: first for x-values, second for y-values respectively. If you have a list of indices in format p=[[x0,y0],[x1,y1], ... ] for the 2d array D, just use indx=tuple(np.transpose(p)) which is ([x0,x1,..],[y0,y1,...]) and access via D[indx].

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