CODEWITHSUNDEEP
pythonlist
Mikhail Shumikhin
Mikhail Shumikhin

Reputation: 21

Remove elements in a list if difference with previous element less than value

Given a list of numbers in ascending order. It is necessary to leave only elements to get such a list where the difference between the elements was greater or equal than a certain value (10 in my case).

Given:

list = [10,15,17,21,34,36,42,67,75,84,92,94,103,115]

Goal:

 list=[10,21,34,67,84,94,115]

Upvotes: 1

Views: 2716

Answers (3)

David Culbreth
David Culbreth

Reputation: 2776

This problem can be solved fairly simply by iterating over your initial set of values, and adding them to your new list only when your difference of x condition is met.

Additionally, by putting this functionality into a function, you can get easily swap out the values or the minimum distance.

values = [10,15,17,21,34,36,42,67,75,84,92,94,103,115]

def foo(elements, distance):
  elements = sorted(elements) # sorting the user input
  new_elements = [elements[0]] # make a new list for output
  for element in elements[1:]: # Iterate over the remaining elements...
    if element - new_elements[-1] >= distance: 
      # this is the condition you described above
      new_elements.append(element)

  return new_elements

print(foo(values, 10))
# >>> [10, 21, 34, 67, 84, 94, 115]
print(foo(values, 5))
# >>> [10, 15, 21, 34, 42, 67, 75, 84, 92, 103, 115]

A few other notes here...

  • I sorted the array before I processed it. You may not want to do that for your particular application, but it seemed to make sense, since your sample data was already sorted. In the case that you don't want to sort the data before you build the list, you can remove the sorted on the line that I commented above.

  • I named the function foo because I was lazy and didn't want to think about the name. I highly recommend that you give it a more descriptive name.

Upvotes: 0

Chris Doyle
Chris Doyle

Reputation: 11992

you could use a while loop and a variable to track the current index you are currently looking at. So starting at index 1, check if the number at this index minus the number in the previous index is less than 10. If it is then delete this index but keep the index counter the same so we look at the next num that is now in this index. If the difference is 10 or more increase the index to look at the next num. I have an additional print line in the loop you can remove this is just to show the comparing.

nums = [10, 15, 17, 21, 34, 36, 42, 67, 75, 84, 92, 94, 103, 115]

index = 1
while index < len(nums):
    print(f"comparing {nums[index-1]} with {nums[index]} nums list {nums}")
    if nums[index] - nums[index - 1] < 10:
        del nums[index]
    else:
        index += 1

print(nums)

OUTPUT

comparing 10 with 15 nums list [10, 15, 17, 21, 34, 36, 42, 67, 75, 84, 92, 94, 103, 115]
comparing 10 with 17 nums list [10, 17, 21, 34, 36, 42, 67, 75, 84, 92, 94, 103, 115]
comparing 10 with 21 nums list [10, 21, 34, 36, 42, 67, 75, 84, 92, 94, 103, 115]
comparing 21 with 34 nums list [10, 21, 34, 36, 42, 67, 75, 84, 92, 94, 103, 115]
comparing 34 with 36 nums list [10, 21, 34, 36, 42, 67, 75, 84, 92, 94, 103, 115]
comparing 34 with 42 nums list [10, 21, 34, 42, 67, 75, 84, 92, 94, 103, 115]
comparing 34 with 67 nums list [10, 21, 34, 67, 75, 84, 92, 94, 103, 115]
comparing 67 with 75 nums list [10, 21, 34, 67, 75, 84, 92, 94, 103, 115]
comparing 67 with 84 nums list [10, 21, 34, 67, 84, 92, 94, 103, 115]
comparing 84 with 92 nums list [10, 21, 34, 67, 84, 92, 94, 103, 115]
comparing 84 with 94 nums list [10, 21, 34, 67, 84, 94, 103, 115]
comparing 94 with 103 nums list [10, 21, 34, 67, 84, 94, 103, 115]
comparing 94 with 115 nums list [10, 21, 34, 67, 84, 94, 115]
[10, 21, 34, 67, 84, 94, 115]

Upvotes: 2

John Coleman
John Coleman

Reputation: 51998

You could build up the list in a loop. Start with the first number in the list. Keep track of the last number chosen to be in the new list. Add an item to the new list only when it differs from the last number chosen by at least the target amount:

my_list = [10,15,17,21,34,36,42,67,75,84,92,94,103,115]

last_num = my_list[0]
new_list = [last_num]

for x in my_list[1:]:
    if x - last_num >= 10:
        new_list.append(x)
        last_num = x

print(new_list) #prints [10, 21, 34, 67, 84, 94, 115]

Upvotes: 0

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