Or, as the Python interpreter reports: Traceback (most recent call last):Ĭsv_mapping_list.sort(key=lambda item: item.get("Age"))Ĭsv_mapping_list = sorted(csv_mapping_list, key=lambda item: item.get("Age"))Īs usual, I appreciate your support. Here, we have to specify the key parameter as dictionaries cannot be naturally sorted. csv_mapping_list.sort(key=lambda item: item.get("Age")) In the following snippet, we sort the list of dictionaries by age. Instead, we can use the builtin sort function for lists. Luckily for us, we don’t have to implement sorting by hand in Python. Pretty cool stuff! Sorting a List of Dictionaries With Sort Function In other words, we create a tuple on the right side of the expression and unpack it on the left side of the expression. Instead, you can use the items() method of the dictionary to return a list of key-value pairs, and then apply enumerate() to the list of key/value pairs. We know that dictionaries are unordered, there is no index to enumerate over. However, you could try using an Ordered Dict (included in Python 2.7+) to get around this. Iterate over all key-value pairs of dictionary by index. You can order the display, but not the keys themselves in the dict. To accomplish the swap, we leverage tuple packing and unpacking. Dictionaries are non-ordered, so there is no simple way to specify the order in which dictionary keys are shown. Since looking into this topic, I’ve found that Python has a nice way of handling the variable swap in a single line of code: size = len(csv_mapping_list)Ĭsv_mapping_list, csv_mapping_list = csv_mapping_list, csv_mapping_listĬlearly, I didn’t pick that great of a variable name for the swap, but you get the idea. To do that, we leverage the “Age” field of each dictionary as seen in line 5. Theres also an items() which returns a list of (key, value) tuples, which is. Here, we’ve sorted the list of dictionaries in place by age. keys() and dict.values() return lists of the keys or values explicitly. If csv_mapping_list > csv_mapping_list:Ĭsv_mapping_list = csv_mapping_list Instead, we’ll leverage one of the more popular algorithms, selection sort: size = len(csv_mapping_list) To sort a list or dictionary by its keys or values in Python, we can use the built-in sorted() function. Sorting is probably one of the most researched areas of Computer Science, so we won’t dive into the philosophy. It’s normal for me to share a brute force method followed by a couple more elegant methods, so take care to skip ahead if needed. SolutionsĪs always, I like to share many possible solutions. Today, I want to focus on sorting a list of dictionaries. In any case, we always have to start with data processing. For instance, maybe older individuals prefer certain colors, or perhaps younger individuals have certain types of names. That way we could plot them in order of increasing or decreasing age to see if we could spot any trends. In this case, we might want to order our data points by age. Likewise, order of the data might matter. In other words, we have our data, but we might want to use a subset of it. Of course, having the data in a nice format and actually using that data for visualization are very different problems. To summarize: itemgetter keeps the execution fully on the C level, so it's as fast as possible.As mentioned before, I was working on parsing a CSV file for data visualization, and I ended up getting everything I wanted in the following format: csv_mapping_list = [ that's a lot more work for the interpreter. sorted(A, key = lambda user: (user, user))įrom the comments: bet there is not a big difference between the two, but itemgetter avoids a bit of overhead because it extracts the keys and make the tuple during a single opcode( CALL_FUNCTION), while calling the lambda will have to call the function, load the various constants(which are other bytecodes) finally call the subscript ( BINARY_SUBSCR), build the tuple and return it. In the following sections, we'll explore different ways to sort a Python dictionary that include: sorting a dictionary by keys sorting a dictionary by values Sorting a dictionary by Keys The first way we can sort a dictionary is by its keys.
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