# 5 Best Ways to Extract Digits from Tuple List in Python

Rate this post

π‘ Problem Formulation: Imagine you have a list of tuples, and each tuple contains a mix of integer digits and potentially other types of data. Your task is to extract only the digit elements from each tuple, and perhaps, collect them into a new list. For example, given the input `[('a', 1, 'b'), (2, 'c'), ('4', 5)]`, the desired output would be a list of extracted digits like `[1, 2, 5]`.

## Method 1: List Comprehension with Type Checking

This method uses list comprehension to iterate through each tuple in the list, and further iterate through each element in the tuple, checking for digit types using the type function, and collecting them into a new list.

Here’s an example:

```data = [('a', 1, 'b'), (2, 'c'), ('4', 5)]
digits = [element for tup in data for element in tup if type(element) == int]
print(digits)
```

Output: `[1, 2, 5]`

The code iterates over every tuple `tup` in the list `data`, and then iterates over every element `element` in each tuple. The list comprehension includes a conditional that only adds `element` to the resultant `digits` list if it is of type `int`, filtering out any non-integer elements.

## Method 2: Regular Expressions

By utilizing Python’s `re` module, you can match numeric patterns within strings. This method involves converting each tuple element into a string and then using regular expressions to find all digits.

Here’s an example:

```import re

data = [('a', '1', 'b'), ('2', 'c'), ('4', 5)]
digit_pattern = re.compile(r'\d+')
digits = [int(match) for tup in data for element in tup if isinstance(element, str) and match in digit_pattern.findall(element)]
print(digits)
```

Output: `[1, 2, 4]`

This block of code first compiles a regular expression pattern to match sequences of digits `r'\d+'`. It then iterates over each string element of the tuples, using the `findall` method of the compiled pattern to extract all digit sequences, converting them into integers and adding them to the final `digits` list.

## Method 3: Using Filter and Lambda

This method combines Python’s `filter` function with a lambda function to specifically check and extract the integer elements from each tuple.

Here’s an example:

```data = [('a', 1, 'b'), (2, 'c'), ('4', 5)]
digits = list(filter(lambda element: type(element) == int, (elem for tup in data for elem in tup)))
print(digits)
```

Output: `[1, 2, 5]`

The snippet creates a flat generator of all elements in all tuples with `(elem for tup in data for elem in tup)`, then filters through this flat list using a lambda function that only allows integers, finally converting the filtered object back into a list of digits.

## Method 4: Loop with isinstance Check

By iterating through each tuple in a traditional for-loop and using the `isinstance` function, you can determine if an element is an integer and then append it to the results list.

Here’s an example:

```data = [('a', 1, 'b'), (2, 'c'), ('4', 5)]
digits = []
for tup in data:
for element in tup:
if isinstance(element, int):
digits.append(element)
print(digits)
```

Output: `[1, 2, 5]`

This code manually loops over each tuple in the list, and within each tuple, it loop over each element. It uses the `isinstance()` method to check whether an element is an integer. If it is, the element gets appended to the `digits` list.

## Bonus One-Liner Method 5: Using itertools.chain() and filter()

To flatten all elements of all tuples into a continuous sequence, you can use `itertools.chain()` in combination with `filter()` to directly get all integer digits.

Here’s an example:

```from itertools import chain

data = [('a', 1, 'b'), (2, 'c'), ('4', 5)]
digits = list(filter(lambda x: isinstance(x, int), chain(*data)))
print(digits)
```

Output: `[1, 2, 5]`

Here, the `chain(*data)` function flattens the list of tuples into one sequence of elements. The `filter()` function, coupled with a lambda, picks out only integers from this flattened list. The result is then converted into a list of digits using `list()`.

## Summary/Discussion

• Method 1: List Comprehension with Type Checking. Strengths: Concise and easy to read. Weaknesses: Might not be efficient for large data sets due to the lack of short-circuiting.
• Method 2: Regular Expressions. Strengths: Powerful when working with string data. Weaknesses: Overhead of converting to string and using regex can be inefficient.
• Method 3: Using Filter and Lambda. Strengths: Functional approach, potentially more efficient. Weaknesses: Can be less readable to those unfamiliar with functional programming concepts.
• Method 4: Loop with isinstance Check. Strengths: Very explicit, easy to understand for beginners. Weaknesses: Verbose and potentially slower for large data sets.
• Bonus Method 5: Using itertools.chain() and filter(). Strengths: Extremely concise and efficient for large data due to iterator use. Weaknesses: Requires understanding itertools and functional programming concepts.