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How do I set the first N elements of an array to zero?

I have a long array:

x= ([2, 5, 4, 7, ...])

for which I need to set the first N

elements to 0

. So for the N = 2

desired output would be:

x = ([0, 0, 4, 7, ...])

Is there an easy way to do this in Python? Some function numpy

?

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2 answers


Pure python:

x[:n] = [0] * n

with numpy:

y = numpy.array(x)
y[0:n] = 0


also note that x[:n] = 0

does n't work if x

is a python list (instead of a numpy array).

It's also a good idea to use [{some object here}] * n

for any mutable, because there won't be n different objects in the list, but n references to the same object:

>>> a = [[],[],[],[]]
>>> a[0:2] = [["a"]] * 2
>>> a
[['a'], ['a'], [], []]
>>> a[0].append("b")
>>> a
[['a', 'b'], ['a', 'b'], [], []]
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Just set them explicitly:



x[0:2] = 0
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