CODEWITHSUNDEEP
pythonlist
deadstump
deadstump

Reputation: 965

Removing unwanted data from lists

I have a list of varying length that I want to continuously up date with some new data. So basically I want to add a new data point and remove any data out of a set range. I have been playing around with this for a little bit now and haven't gotten anywhere that I can tell. I was trying to use this post as a reference, but apparently I don't under stand what is going on. Below is a code snippet that is an example of what I have tried.

for i in range(0,100):
    n.append(i)
    n = [x for x in n if not (x-n[-1]>10)]
    print len(n)

Ideally n would only have the last 10 data points contained in it at any given time during the for loop. I am sure that this is something basic that I am just not understanding, if you all could help me out I would really appreciate it. Thanks.

Edit: Example of the list n

[0]
[0, 1]
...
[89, 90, 91, 92, 93, 94, 95, 96, 97, 99]

Upvotes: 0

Views: 243

Answers (4)

root
root

Reputation: 80406

use deque with fast appends and pops: and from python 2.7 up you can set maxlen.

from collections import deque

>>> d=deque([])
>>> for i in range(10):
...     d.append(i)
...     if len(d) > 3: d.popleft()
... 
0
1
2
3
4
5
6
>>> d
deque([7, 8, 9])

Using maxlen:

>>> d = deque(range(5), maxlen=3)
>>> print d
deque([2, 3, 4], maxlen=3)
>>> print d.maxlen
3

Upvotes: 0

Iliyan Bobev
Iliyan Bobev

Reputation: 3108

If I properly understand, you want to keep some variable number of elements in the list "n". Let's call that variable "m", so

for i in range(0,100):
    n.append(i)
    m = random.randint(1, 10)
    if len(n)>m:
        n = n[-m:]               # [-m:] defines the last m elements of n
    print len(n)

This should always print m in the end

Upvotes: 1

Kaustubh Karkare
Kaustubh Karkare

Reputation: 1101

Assuming you mean that n should contain only the latest 10 data points inserted, you want:

for i in range(0,100):
    n.append(i)
    if len(n)>10: n[:] = n[1:]
    print len(n) # will never go above 10

Upvotes: 4

Colleen
Colleen

Reputation: 25499

Why not just pop() the list every time you append something, if len>10? If I'm understanding the question right.

for i in range(0,100):
    n.append(i)
    if len(n)>10:
       n.pop(0)

Upvotes: 4

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