How to make a list of lists in python

Question

I am trying to make a list of lists in python using random.random().

def takeStep(prevPosition, maxStep):

    """simulates taking a step between positive and negative maxStep, \
adds it to prevPosition and returns next position"""

    nextPosition = prevPosition + (-maxStep + \
                     ( maxStep - (-maxStep)) * random.random())

list500Steps = []

list1000Walks = []

for kk in range(0,1000):

    list1000Walks.append(list500Steps)


    for jj in range(0 , 500):

        list500Steps.append(list500Steps[-1] + takeStep(0 , MAX_STEP_SIZE))

I know why this gives me what it does, just don't know how to do something about it. Please give the simplest answer, in new at this and don't know a lot yet.

Aside: it's usually a bad idea to hardcode parameters like "1000" into your variable names. — DSM
– DSM, Commented Mar 5, 2013 at 3:53

IamAlexAlright · Accepted Answer · 2013-03-05 03:21:54Z

1

for kk in xrange(0,1000):
    list500steps = []
    for jj in range(0,500):
         list500steps.append(...)
    list1000walks.append(list500steps)

Notice how I am creating an empty array (list500steps) each time in the first for loop? Then, after creating all the steps I append that array (Which is now NOT empty) to the array of walks.

answered Mar 5, 2013 at 3:21

IamAlexAlright

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Comments

Keith Aylwin · Accepted Answer · 2013-03-05 03:49:08Z

0

 import random

 def takeStep(prevPosition, maxStep):

     """simulates taking a step between positive and negative maxStep, \
      adds it to prevPosition and returns next position"""

      nextPosition = prevPosition + (-maxStep + \
      ( maxStep - (-maxStep)) * random.random())
       return nextPosition # You didn't have this, I'm not exactly sure what you were going for         #but I think this is it
#Without this statement it will repeatedly crash

list500Steps = [0] 
list1000Walks = [0]
#The zeros are place holders so for the for loop (jj) below. That way 
#The first time it goes through the for loop it has something to index-
#during "list500Steps.append(list500Steps[-1] <-- that will draw an eror without anything
#in the loops. I don't know if that was your problem but it isn't good either way



for kk in range(0,1000):
    list1000Walks.append(list500Steps)


for jj in range(0 , 500):
    list500Steps.append(list500Steps[-1] + takeStep(0 , MAX_STEP_SIZE)) 
 #I hope for MAX_STEP_SIZE you intend on (a) defining the variable (b) inputing in a number

You might want to print one of the lists to check the input.

answered Mar 5, 2013 at 3:49

Keith Aylwin

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1 Comment

user2134116 Over a year ago

this makes sense as well. I just forgot to paste the return for the function on the forum. Thanks again for the help!

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How to make a list of lists in python

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You might want to print one of the lists to check the input.

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You might want to print one of the lists to check the input.

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