I've searched for a relevant thread on how to do this but I cannot find anything.
I have an array:
x = [a,a,a,b,a,a]
I want to copy the elements of the array into a new array until I find 'b'. I tried to do this with a loop but I get an error that "y is not defined", I tried initializing y but that didn't work either. Any ideas? I'm sure there is a better way to do this.
for ii in x:
if x[ii].find(num) == 0:
break
else:
y[ii] = x[ii]
Try this:
x = [1,1,1,2,1,1]
b = 2
try:
y = x[:x.index(b)]
except ValueError:
y = x[:]
For example:
In [10]: x = [1,1,1,2,1,1]
...: b = 2
...:
...: try:
...: y = x[:x.index(b)]
...: except ValueError:
...: # b was not found in x. Just copy the whole thing.
...: y = x[:]
...:
In [11]: y
Out[11]: [1, 1, 1]
See list.index() and the shallow-copy slice for more information.
y = []
for e in x:
if e == 2:
break
y.append(e)
?
y = x[:x.index(2)].
You could use itertools.takewhile:
>>> x = [1,1,1,2,1,1]
>>> import itertools
>>> y = list(itertools.takewhile(lambda i: i != 2, x))
>>> y
[1, 1, 1]
When using a loop, you have to use y.append; if you do y[ii] = ..., then you will get an IndexError as you try to set e.g. the first element of an array that has zero elements. Also, when you loop like this for ii in x: then ii is already the element from x, i.e. you do not have to do x[ii]. In your case, this did not give an exception, since x[1] would be a valid element of x, but it would not be what you expected.
I would split the array by the b index:
>>> x = ['a','a','a','b','a','a']
>>> c = x.index('b')
>>> x[:c]
['a', 'a', 'a']
>>> x[c:]
['b', 'a', 'a']
Way to get things done with generator expression:
x = ['a', 'a', 'a', 'b', 'a', 'a']
items = list(next(iter([])) if item == 'b' else item for item in x)
print items
['a', 'a', 'a']
next(iter([])) to trigger StopIteration in a list comprehension. I'm not sure whether I should upvote this, but certainly a creative solution. ;-)
Though it is somehow similar to Will's answer, but in here it shows the use of slice built-in slicing object:
>>> x = ['a','a','a','b','a','a']
>>> s = slice(x.index('b'))
>>>
>>> x[s]
['a', 'a', 'a']
x[ii].find(num)? You have a list of integers or strings?