I cant see if my list has repeated numbers in it

Question

I'm trying to generate 20 random numbers in my list. Next I want to see if there are any repeated numbers in it.

I generated the random numbers. Next I did an insertion sort in order to arrange the list in a growing order. To see if I had any repeated numbers, I iterated over the list and if the previous number was equal to the next number, then my list had repeated numbers in it.

import random

random_array=[]

def array():
  for i in range(0,20):
    random_element=random.randint(1,35)
    random_array.append(random_element)
  return random_array
print(array())

# function to order the list
def insertion_sort():
  for i in range(1,len(random_array)):
    while i>0 and random_array[i-1]>random_array[i]:
      random_array[i-1],random_array[i]=random_array[i],random_array[i-1]
      i=i-1
  return random_array
print(insertion_sort())

def verification():
  for i in random_array:
    insertion_sort()
    if i-1==i:
      return True
    else:
      return False
print(verification())

My program always returns false independent of the generated list.

if the number in that position is equal to the number in the next position then there are repeated numbers — Luismaia1994, Jun 13 '19 at 15:40
you are not iterating over the indexes, rather you are iterating over elements,fix up your for loop, also why are you calling insertion_sort in the loop? — Devesh Kumar Singh, Jun 13 '19 at 15:41
what i wrote is the same as for i in range(0,len(random_array): if random_array(i-1)==random_array(i).... — Luismaia1994, Jun 13 '19 at 15:42
@Luismaia1994, no it is not the same. i-1 does not refer to the element at the previous index, it resolves to the index value less 1. — Conor Retra, Jun 13 '19 at 15:45
1) `if random_array[i-1]==random_array[i]` is different from `if random_array(i-1)==random_array(i)` and is different from `if i-1==i`; 2) you don't need to run `insertion_sort()` in every iteration. You just need run `array()` and `insertion_sort()` once before `for` loop — JoYSword, Jun 13 '19 at 15:48
also you are returning at the first mismatch you get, put your return outside for loop — Devesh Kumar Singh, Jun 13 '19 at 15:48
Not to be rude, but there are quite a few issues with your verification algorithm. If your goal is just to check if you have any duplicates, use `if len(set(random_array)) == len(random_array): return True` — Conor Retra, Jun 13 '19 at 15:54

score 1 · Answer 1 · answered Jun 13 '19 at 15:53

Issues in your code:

You are iterating on the elements and subtracting them and comparing, instead you should iterate on the indexes and use them to compare consecutive elements
You are calling insertion_sort() within your for loop, I assume by mistake
You want to break the for loop on the first match you found, and in the end return a boolean which tells if the match has happened or not

So your code will look like

def verification():
    #Flag to keep track of matches
    flag = False
    #Iterate over list via indexes
    for i in range(len(random_array)):
        #If consecutive elements match, set flag to true and break loop
        if random_array[i-1]==random_array[i]:
            flag = True
            break
    #Return flag value
    return flag

score 0 · Answer 2 · answered Jun 13 '19 at 15:49

You have two options here: If you don't care about the order, you can use set which is a data type that can only have unique elements. If you need to keep your original order of numbers, you need to use OrderedDict from collections

See this stack answer: https://stackoverflow.com/a/7961393/11323304

ncica · Answer 3 · 2019-06-13T15:55:10.483

your loop in def verification(): is exiting after first iteration because if else: return False (it's exiting)

use simple flag:

import random

random_array=[]

def array():
  for i in range(0,20):
    random_element=random.randint(1,35)
    random_array.append(random_element)
  return random_array
print(array())

# function to order the list
def insertion_sort():
  for i in range(1,len(random_array)):
    while i>0 and random_array[i-1]>random_array[i]:
      random_array[i-1],random_array[i]=random_array[i],random_array[i-1]
      i=i-1
  return random_array
print(insertion_sort())

def verification():
  #for i in random_array:
  status = False # <----
  for i in range(len(random_array)-1): # <------
    insertion_sort()
    #if i-1==i:
    if random_array[i] == random_array[i+1]: # Iterate over list by indexes
      status = True
      break 
  return status
print(verification())

score 0 · Answer 4 · answered Jun 13 '19 at 15:49

Your verification function is wrong. You are comparing the value of element i to the value of element i - 1, which is never going to be true. Try this:

insertion_sort()
for i in range(1,len(random_array - 1)):
    if random_arry[i] == random_array[i-1]:
        return True
return False  # If you get through every element without finding a match, return False

score 0 · Accepted Answer · answered Jun 13 '19 at 15:50

0

You can do it with much shorter code using itertools.Counter:

import random
from collections import Counter

# Generate a random array
random_array = [random.randint(1, 35) for _ in range(20)]


nums = [
    n  # A number
    for (n, count) in Counter(random_array).items()  # From countered items
    if count > 1  # If the count of this number is more than one
]
print(nums)

answered Jun 13 '19 at 15:50

vurmux

9,420
3
25
45

the goal also is to understand functions. I'm not interest in shorter codes yet. I know there are much easier ways to do the problem.. – Luismaia1994 Jun 14 '19 at 22:44

I cant see if my list has repeated numbers in it

5 Answers5