Given array=[1, 2, 3, 4, 5, 6]
I want to choose the 0-th 2-nd, 4-th index value to build a new array
array1=[1, 3, 5]
Could someone show me how to do using python? Thanks~
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2 Answers
If it is just 0, 2, and 4, you can use operator.itemgetter():
from operator import itemgetter
array1 = itemgetter(0, 2, 4)(array)
That will be a tuple. If it must be a list, convert it:
array1 = list(itemgetter(0, 2, 4)(array))
If the point is to get the even numbered indices, use slicing:
array1 = array[::2]
Whichever you are looking for, you could use a list comprehension:
array1 = [array[i] for i in (0, 2, 4)]
or
array1 = [array[i] for i in xrange(0, len(array), 2)]
3 Comments
Echo0831
Thanks very much~ If I want to set the "step",which is the picking interval, how could I do? For example, I want to pick elements at 0,3,6 indices or 0,4,8~
kanayamalakar
@Echo0831, you can achieve that by writing
array1 = [array[i] for i in xrange(start, len(array), step)], where start should be the index of the first element and step is the step size. Or you can see my answer.
zondo
@Echo0831: When I say
array[::2], that means all items in array from one end to the other with a step of 2. Therefore, you can just change the 2 to whatever step you want. In array1 = [array[i] for i in xrange(0, len(array), 2)], I say to go from an index of 0, the first element, to the index of the length of the array - 1, the last element, with a step of 2. Therefore, you can change the 2 to whatever step you want.You can try something like this. In python the nth term of a list has index (n-1). Suppose the first element you want is 2, which happens to be the element 1 of array. Just save the first element index in a variable. Append it to the new list array1 and increase the index by 2. Continue doing this until the list array is exhausted.
from numpy import*
array=[1,2,3,4,5,6]
array1=[]
term=1
while term<len(array): # if the array length is 6 then it will have upto element 5.
array1.append(array[term])
term=term+2 # 2 is the gap between elements. You can replace it with your required step size.
1 Comment
Echo0831
Got you! make sense~