Reputation: 15
I'm trying to generate a random dataset to plot a graph in Python 2.7.
In which the 'y' list stores 14 integers between 100 and 135. I did that using the following code:
y = [random.randint(100, 135) for i in xrange(14)]
And for the 'x' list, I wanted to store the index values of the elements in 'y'. To achieve this, I tried using the code:
x = []
for i in y:
pt = y.index(i)
x.append(pt)
But when I run this, the result of the for loop ends up being:
x = [0, 1, 1, 3, 4, 5, 6, 3, 1, 9, 1, 11, 12, 13]
Why isn't the result the following?
x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
Upvotes: 0
Views: 73
Reputation: 2477
Python is returning the first location of a value in y.
Running your code, here's an example y
:
[127, 124, 105, 119, 121, 118, 130, 123, 122, 105, 110, 109, 108, 110]
110 is at both 10 and 13. 105 is at both 2 and 9. Python stops looking after it finds the first one, so x
then becomes:
[0, 1, 2, 3, 4, 5, 6, 7, 8, 2, 10, 11, 12, 10]
Upvotes: 1
Reputation: 49330
list.index()
finds the index of the first occurrence of that object in the list
, which produces the results you saw when the list
has repeated elements. Something like [1, 1, 1].index(1)
would produce 0
.
If you want to generate a list of indices, you can use list(range(len(y)))
, which finds the length of y
, creates a range()
object out of it, then creates a list
out of that object. Since you're using Python 2, you can omit the list()
call, since Python 2's range()
will already return a list
.
Upvotes: 0