Array initialization in Python

Question

I want to initialize an array with 10 values starting at X and incrementing by Y. I cannot directly use range() as it requires to give the maximum value, not the number of values.

I can do this in a loop, as follows:

a = []
v = X
for i in range(10):
    a.append(v)
    v = v + Y

But I'm certain there's a cute python one liner to do this ...

Solution 1

>>> x = 2
>>> y = 3
>>> [i*y + x for i in range(10)]
[2, 5, 8, 11, 14, 17, 20, 23, 26, 29]

Solution 2

You can use this:

>>> x = 3
>>> y = 4
>>> range(x, x+10*y, y)

[3, 7, 11, 15, 19, 23, 27, 31, 35, 39]

Solution 3

Just another way of doing it

Y=6
X=10
N=10
[y for x,y in zip(range(0,N),itertools.count(X,Y))]
[10, 16, 22, 28, 34, 40, 46, 52, 58, 64]

And yet another way

map(lambda (x,y):y,zip(range(0,N),itertools.count(10,Y)))
[10, 16, 22, 28, 34, 40, 46, 52, 58, 64]

And yet another way

import numpy
numpy.array(range(0,N))*Y+X
array([10, 16, 22, 28, 34, 40, 46, 52, 58, 64])

And even this

C=itertools.count(10,Y)
[C.next() for i in xrange(10)]
[10, 16, 22, 28, 34, 40, 46, 52, 58, 64]

Solution 4

[x+i*y for i in xrange(1,10)]

will do the job

Solution 5

If I understood your question correctly:

Y = 6
a = [x + Y for x in range(10)]

Edit: Oh, I see I misunderstood the question. Carry on.

View more solutions

Comments

[Michael J. Barber]

never try this with floats as x and y

[eumiro]

numpy.array(range…)? Have a look at numpy.arange

[WestCoastProjects]

The np.arange(0,N) *Y+X is useful.