Jake Schurch - 10 months ago 54

Python Question

Sorry for creating this question but I have been stuck on this question for a while.

Basically I'm trying to take a list:

`numbers=[1, 2, -1, -2, 4, 5]`

And subset this list into a list of list that display positive/negative movements (or trends)

The end result is to have:

`subset_list = [[1, 2], [-1, -2], [4, 5]]`

Basically I have been using nested while functions to append a positive movement to the subset, and when the condition is not met, the subset is appended to subset_list and then evaluates if there is a negative movement.

I keep getting an

`IndexError`

`subset_list`

`[[1, 2]]`

Here is my code:

`numbers = [1,2,-1,-2,4,5]`

subset = []

subset_list = []

subset.append(numbers[0])

i = 1

while i < (len(numbers)):

if numbers[i] <= numbers[i+1]:

subset.append(numbers[i])

i+= 1

while subset[-1] <= numbers[i] or numbers[i] <= numbers[i+1]:

subset.append(numbers[i])

i += 1

subset_list.append(subset)

subset = []

i += 1

if numbers[i] > numbers[i+1]:

subset.append(numbers[i])

i+= 1

while subset[-1] <= numbers[i] or numbers[i] <= numbers[i+1]:

subset.append(numbers[i])

i+= 1

subset_list.append(subset)

subset = []

i += 1

Thanks!

-Jake

Answer

Here is a way to re-write this:

```
numbers=[1,2,-1,-2,4,5]
direction = True # positive or negative
prevdirection = True
res = [[numbers[0]]]
for previtem, item in zip(numbers[:-1], numbers[1:]):
direction = True if item - previtem > 0 else False
if direction != prevdirection:
res.append([])
prevdirection = direction
res[-1].append(item)
print(res)
```

Source (Stackoverflow)