Python: A program to find the LENGTH of the longest run in a given list?

Question

Q: A run is a sequence of adjacent repeated values. Given a list, write a function to determine the length of the longest run. For example, for the sequence [1, 2, 5, 5, 3,

Answer 1

This should work if you do not want to use itertools and imports.

a=[1, 2, 5, 5, 3, 1, 2, 4, 3, 2, 2, 2, 2, 3, 6, 5, 5, 6, 3, 1]

def longestrun(myList):
    result = None
    prev = None
    size = 0
    max_size = 0


    for i in myList:
        if i == prev:
            print (i)
            size += 1
            if size > max_size:
                print ('*******  '+ str(max_size))
                max_size = size 
        else:
            size = 0
        prev = i
    print (max_size+1)    
    return max_size+1


longestrun(a)

Answer 2

def getSublists(L,n):
    outL=[]
    for i in range(0,len(L)-n+1):
        outL.append(L[i:i+n])
    return outL


def longestRun(L):
    for n in range(len(L), 0, -1):
        temp=getSublists(L,n)
        for subL in temp:
            if subL==sorted(subL):
                return len(subL)

Answer 3

Just another way of doing it:

def longestrun(myList):
    sett = set()
    size = 1
    for ind, elm in enumerate(myList):
        if ind > 0:
            if elm == myList[ind - 1]:
                size += 1
            else:
                sett.update([size])
                size = 1
    sett.update([size])
    return max(sett)

myList = [1, 2, 5, 5, 3, 1, 2, 4, 3, 2, 2, 2, 2, 3, 6, 5, 5, 6, 3, 1]
print longestrun(myList)

Answer 4

As an update to David Robinson's answer, it is now (Python 3.4) possible to return 0 on an empty sequence (instead of raising ValueError):

import itertools
max((sum(1 for _ in l) for n, l in itertools.groupby(lst)), default=0)

Answer 5

You can do this in one line using itertools.groupby:

import itertools
max(sum(1 for _ in l) for n, l in itertools.groupby(lst))

Answer 6

def longestrun(myList):
    size = 1
    max_size = 0
    for i in range(len(myList)-1):
        if myList[i+1] = myList[i]:
            size += 1
        else: 
            size = 1
        if max_size<size:
            max_size = size
    return size 

Remove the .split() from myList in main() and you're good to go with this.