Repeating each element of a numpy array 5 times
import numpy as np
data = np.arange(-50,50,10)
print data
[-50 -40 -30 -20 -10 0 10 20 30 40]
I want to repeat each element of data 5 times and make new array as follows:
ans = [-50 -50 -50 -50 -50 -40 -40 ... 40]
How can I do it?
What about repeating the whole array 5 times?
ans = [-50 -40 -30 -20 -10 0 10 20 30 40 -50 -40 -30 -20 -10 0 10 20 30 40 -50 -40 -30 -20 -10 0 10 20 30 40 -50 -40 -30 -20 -10 0 10 20 30 40 -50 -40 -30 -20 -10 0 10 20 30 40 .......]
Solution 1:
In [1]: data = np.arange(-50,50,10)
To repeat each element 5 times use np.repeat:
In [3]: np.repeat(data, 5)
Out[3]:
array([-50, -50, -50, -50, -50, -40, -40, -40, -40, -40, -30, -30, -30,
-30, -30, -20, -20, -20, -20, -20, -10, -10, -10, -10, -10, 0,
0, 0, 0, 0, 10, 10, 10, 10, 10, 20, 20, 20, 20,
20, 30, 30, 30, 30, 30, 40, 40, 40, 40, 40])
To repeat the array 5 times use np.tile:
In [2]: np.tile(data, 5)
Out[2]:
array([-50, -40, -30, -20, -10, 0, 10, 20, 30, 40, -50, -40, -30,
-20, -10, 0, 10, 20, 30, 40, -50, -40, -30, -20, -10, 0,
10, 20, 30, 40, -50, -40, -30, -20, -10, 0, 10, 20, 30,
40, -50, -40, -30, -20, -10, 0, 10, 20, 30, 40])
Note, however, that sometimes you can take advantage of NumPy broadcasting instead of creating a larger array with repeated elements.
For example, if
z = np.array([1, 2])
v = np.array([[3], [4], [5]])
then to add these arrays to produce
[[4 5]
[5 6]
[6 7]]
you do not need to use tile:
In [12]: np.tile(z, (3,1))
Out[12]:
array([[1, 2],
[1, 2],
[1, 2]])
In [13]: np.tile(v, (1,2))
Out[13]:
array([[3, 3],
[4, 4],
[5, 5]])
In [14]: np.tile(z, (3,1)) + np.tile(v, (1,2))
Out[14]:
array([[4, 5],
[5, 6],
[6, 7]])
Instead, NumPy will broadcast the arrays for you:
In [15]: z + v
Out[15]:
array([[4, 5],
[5, 6],
[6, 7]])
Solution 2:
Simply use np.repeat
:
In [5]: data.repeat(5)
Out[5]:
array([-50, -50, -50, -50, -50, -40, -40, -40, -40, -40, -30, -30, -30,
-30, -30, -20, -20, -20, -20, -20, -10, -10, -10, -10, -10, 0,
0, 0, 0, 0, 10, 10, 10, 10, 10, 20, 20, 20, 20,
20, 30, 30, 30, 30, 30, 40, 40, 40, 40, 40])