The standard way of checking if an element exists in a list is to use the in keyword. For example, ‘Alice’ in [1, ‘Alice’, 3] will return True while the same returns False for ‘Bob’. If you need to check more complicated conditions, use the any(condition(x) for x in list) function with a generator expression. … Read more
Answer: The simplest, most straightforward, and most readable way to convert a list to a tuple is Python’s built-in tuple(list) function. You can pass any iterable (such as a list, another tuple, or a set) as an argument into this so-called constructor function and it returns a new tuple data structure that contains all elements … Read more
To convert a list lst of strings to a string, use the ”.join(lst) method with an empty separator string between the elements. If you have a list of objects, first convert each element to a string and join the result with the generator expression ”.join(str(x) for x in lst). Problem: Given a list of elements. … Read more
If you’re like me, you may have asked yourself the following question: Why is it string.join(list) instead of list.join(string) in Python? ? The join method works with any iterable, not just with lists. Therefore, you’d have to implement it in hundreds of classes instead of just one (in the string class). Additionally, join() works only … Read more
The most Pythonic way to concatenate a list of objects is the expression ”.join(str(x) for x in lst) that converts each object to a string using the built-in str(…) function in a generator expression. You can concatenate the resulting list of strings using the join() method on the empty string as a delimiter. The result … Read more
To join a list of DataFrames, say dfs, use the pandas.concat(dfs) function that merges an arbitrary number of DataFrames to a single one. When browsing StackOverflow, I recently stumbled upon the following interesting problem. By thinking about solutions to those small data science problems, you can improve your data science skills, so let’s dive into … Read more
To extract elements with specific indices from a Python list, use slicing list[start:stop:step]. If you cannot use slicing because there’s no pattern in the indices you want to access, use the list comprehension statement [lst[i] for i in indices], assuming your indices are stored in the variable indices. People always want to know the most … Read more
To convert a Python list to a NumPy array, use either of the following two methods: Exercise: Create array b from array a using both methods. Then change a value in array a. What happens at array b? NumPy vs Python Lists The Python built-in list data type is powerful. However, the NumPy array has … Read more
To join specific list elements (e.g., with indices 0, 2, and 4) and return the joined string that’s the concatenation of all those, use the expression ”.join([lst[i] for i in [0, 2, 4]]). The list comprehension statement creates a list consisting of elements lst[0], lst[2], and lst[4]. The ”.join() method concatenates those elements using the … Read more
To join and replace all strings in a list lst between start index 1 and end index 5, use the one-liner lst[1:5] = [”.join(lst[1:5])]. This solution is based on slice assignment that selects the slice you want to replace on the left and the values to replace it on the right side of the assignment. … Read more
Given a list of strings. Join the first with the second string, the second with the third, and so on. The one-liner [lst[i] + lst[i+1] for i in range(0, len(lst), 2)] solves the problem by using the range function to iterate over every other index i=0, 2, 4, 5, … to concatenate the i-th and … Read more
🛑 Note: Python has zero-based indexing, i.e., the index of the first element is 0, and the index of the i-th element is (i-1). Not considering zero-based indexing but assuming the i-th element has index i is a common source of bugs! Here’s an example that demonstrates how list indexing works in Python: 🏃 Training … Read more