How to Efficiently Append Multiple Values to a Dictionary Key in Python?

Appending Multiple Values to a Dictionary Key

Often, when working with dictionaries, you may encounter situations where you need to append multiple values to a single key. While the traditional approach using a key-value pair structure can suffice, there are more efficient and organized methods.

Let's consider a scenario where you have a list of years and their corresponding values. You want to create a dictionary where the years serve as keys, and the associated values are stored in an array for each year.

For this, a refined solution would be to utilize a nested data structure. Instead of directly assigning a value to a key, you can create an array at that key and append the values accordingly. Here's how it can be achieved:

<code class="python">years_dict = dict()

for line in list:
    if line[0] in years_dict:
        # Append the new value to the existing array at this slot
        years_dict[line[0]].append(line[1])
    else:
        # Create a new array in this slot
        years_dict[line[0]] = [line[1]]</code>

This approach generates a dictionary structured as follows:

{
    "2010": [2],
    "2009": [4, 7],
    "1989": [8]
}

By utilizing a nested structure, you can efficiently append multiple values to a single key, resulting in a more organized and maintainable data representation.

Note that it is generally considered poor practice to create parallel arrays, where elements are associated based solely on their indices. This approach can lead to data inconsistency and maintenance challenges. Instead, it's recommended to use a proper container that encompasses both the keys and values within a single structure.

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