python - Finding items that occur exactly once in an array

Python - Finding items that occur exactly once in an array

To find items that occur exactly once in an array, you can use Python's collections.Counter class to count the occurrences of each item, and then filter out the items that occur exactly once.

Here's a step-by-step guide and a code example to demonstrate this:

Step-by-Step Guide

  1. Import the Counter class from the collections module.
  2. Count the occurrences of each item in the array using Counter.
  3. Filter the items that occur exactly once by iterating through the counts.

Example

from collections import Counter def find_unique_items(array): # Step 1: Count occurrences of each item counts = Counter(array) # Step 2: Filter items that occur exactly once unique_items = [item for item, count in counts.items() if count == 1] return unique_items # Example usage array = [1, 2, 2, 3, 4, 4, 5, 6, 7, 7, 8, 9, 9] unique_items = find_unique_items(array) print(f"Items that occur exactly once: {unique_items}")

Detailed Explanation

  1. Importing Counter:

    from collections import Counter

  2. Counting Occurrences:

    • Counter(array) returns a dictionary-like object where keys are the elements from the array and values are their respective counts.
    counts = Counter(array)

  3. Filtering Unique Items:

    • Using a list comprehension, iterate through the items and counts in the Counter object.
    • Check if the count is equal to 1 and include those items in the resulting list.
    unique_items = [item for item, count in counts.items() if count == 1]

Example Execution

Given the array [1, 2, 2, 3, 4, 4, 5, 6, 7, 7, 8, 9, 9], the function will output:

Items that occur exactly once: [1, 3, 5, 6, 8]

Summary

By using the collections.Counter class and list comprehension, you can efficiently find items that occur exactly once in an array. This approach is concise and leverages Python's built-in capabilities for handling collections.

Examples

  1. Python find elements occurring exactly once in list

    • Description: Shows how to find elements that occur exactly once in a Python list.
    • Code:
      # Example Python code from collections import Counter def find_single_occurrences(arr): counts = Counter(arr) return [item for item, count in counts.items() if count == 1] # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Elements occurring exactly once:", result)

  2. Python list find items occurring once

    • Description: Demonstrates a method to identify items that appear exactly once in a Python list.
    • Code:
      # Example Python code def find_single_occurrences(arr): singles = [] for item in arr: if arr.count(item) == 1 and item not in singles: singles.append(item) return singles # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Items occurring exactly once:", result)

  3. Python find unique elements in list

    • Description: Shows how to find unique elements that occur only once in a Python list.
    • Code:
      # Example Python code def find_single_occurrences(arr): unique = [] for item in set(arr): if arr.count(item) == 1: unique.append(item) return unique # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Unique elements occurring exactly once:", result)

  4. Python list items occurring exactly once

    • Description: Provides a function to find items in a list that occur exactly once using Python.
    • Code:
      # Example Python code def find_single_occurrences(arr): counts = {} for item in arr: counts[item] = counts.get(item, 0) + 1 return [item for item, count in counts.items() if count == 1] # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Items occurring exactly once:", result)

  5. Python find elements with single occurrence

    • Description: Demonstrates how to find elements with a single occurrence in a Python list efficiently.
    • Code:
      # Example Python code def find_single_occurrences(arr): seen_once = set() seen_multiple = set() for item in arr: if item in seen_multiple: continue if item in seen_once: seen_once.remove(item) seen_multiple.add(item) else: seen_once.add(item) return list(seen_once) # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Elements with single occurrence:", result)

  6. Python count elements occurring once in list

    • Description: Provides a method to count and retrieve elements that occur exactly once in a Python list.
    • Code:
      # Example Python code from collections import Counter def find_single_occurrences(arr): counts = Counter(arr) return [item for item, count in counts.items() if count == 1] # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Elements occurring exactly once:", result)

  7. Python find unique items in list occurring once

    • Description: Shows how to find unique items that occur exactly once in a Python list.
    • Code:
      # Example Python code def find_single_occurrences(arr): unique = [] for item in set(arr): if arr.count(item) == 1: unique.append(item) return unique # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Unique items occurring exactly once:", result)

  8. Python get items with single occurrence in list

    • Description: Provides a function to retrieve items with a single occurrence in a Python list.
    • Code:
      # Example Python code def find_single_occurrences(arr): singles = [] for item in arr: if arr.count(item) == 1 and item not in singles: singles.append(item) return singles # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Items with single occurrence:", result)

  9. Python find elements appearing once in list

    • Description: Demonstrates how to find elements in a Python list that appear exactly once.
    • Code:
      # Example Python code def find_single_occurrences(arr): singles = [] for item in arr: if arr.count(item) == 1: singles.append(item) return singles # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Elements appearing exactly once:", result)

  10. Python find elements with only one occurrence

    • Description: Provides a method to find elements in a Python list that have only one occurrence.
    • Code:
      # Example Python code from collections import Counter def find_single_occurrences(arr): counts = Counter(arr) return [item for item, count in counts.items() if count == 1] # Usage example arr = [1, 2, 2, 3, 4, 4, 5, 6, 6] result = find_single_occurrences(arr) print("Elements with only one occurrence:", result)

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