Groupby is a pretty simple concept. We can create a grouping of categories and apply a function to the categories. It’s a simple concept but it’s an extremely valuable technique that’s widely used in data science. In real data science projects, you’ll be dealing with large amounts of data and trying things over and over, so for efficiency, we use Groupby concept. Groupby concept is really important because it’s ability to aggregate data efficiently, both in performance and the amount code is magnificent. Groupby mainly refers to a process involving one or more of the following steps they are:
- Splitting : It is a process in which we split data into group by applying some conditions on datasets.
- Applying : It is a process in which we apply a function to each group independently
- Combining : It is a process in which we combine different datasets after applying groupby and results into a data structure
The following image will help in understanding a process involve in Groupby concept.
1. Group the unique values from the Team column
2. Now there’s a bucket for each group
3. Toss the other data into the buckets
4. Apply a function on the weight column of each bucket.
Splitting Data into Groups
Splitting is a process in which we split data into a group by applying some conditions on datasets. In order to split the data, we apply certain conditions on datasets. In order to split the data, we use
groupby() function this function is used to split the data into groups based on some criteria. Pandas objects can be split on any of their axes. The abstract definition of grouping is to provide a mapping of labels to group names. Pandas datasets can be split into any of their objects. There are multiple ways to split data like:
- obj.groupby(key, axis=1)
- obj.groupby([key1, key2])
Note :In this we refer to the grouping objects as the keys.
Grouping data with one key:
In order to group data with one key, we pass only one key as an argument in
Now we group a data of
Now we print the first entries in all the groups formed.
Grouping data with multiple keys :
In order to group data with multiple keys, we pass multiple keys in
Now we group a data of “Name” and “Qualification” together using multiple keys in
Grouping data by sorting keys :
Group keys are sorted by default uring the groupby operation. User can pass
sort=False for potential speedups.
Now we apply
groupby() without sort
Now we apply
groupby() using sort in order to attain potential speedups
Grouping data with object attributes :
Groups attribute is like dictionary whose keys are the computed unique groups and corresponding values being the axis labels belonging to each group.
Now we group data like we do in a dictionary using keys.
Iterating through groups
In order to iterate an element of groups, we can iterate through the object similar to itertools.obj.
Now we iterate an element of group in a similar way we do in itertools.obj.
Now we iterate an element of group containing multiple keys
As shown in output that group name will be tuple
Selecting a groups
In order to select a group, we can select group using
GroupBy.get_group(). We can select a group by applying a function
GroupBy.get_group this function select a single group.
Now we select a single group using
Now we select an object grouped on multiple columns
Applying function to group
After splitting a data into a group, we apply a function to each group in order to do that we perform some operation they are:
- Aggregation : It is a process in which we compute a summary statistic (or statistics) about each group. For Example, Compute group sums ormeans
- Transformation : It is a process in which we perform some group-specific computations and return a like-indexed. For Example, Filling NAs within groups with a value derived from each group
- Filtration : It is a process in which we discard some groups, according to a group-wise computation that evaluates True or False. For Example, Filtering out data based on the group sum or mean
Aggregation is a process in which we compute a summary statistic about each group. Aggregated function returns a single aggregated value for each group. After splitting a data into groups using
groupby function, several aggregation operations can be performed on the grouped data.
Code #1: Using aggregation via the aggregate method
Now we perform aggregation using aggregate method
Now we perform aggregation on agroup containing multiple keys
Applying multiple functions at once :
We can apply a multiple functions at once by passing a list or dictionary of functions to do aggregation with, outputting a DataFrame.
Now we apply a multiple functions by passing a list of functions.
Applying different functions to DataFrame columns :
In order to apply a different aggregation to the columns of a DataFrame, we can pass a dictionary to aggregate .
Now we apply a different aggregation to the columns of a dataframe.
Transformation is a process in which we perform some group-specific computations and return a like-indexed. Transform method returns an object that is indexed the same (same size) as the one being grouped. The transform function must:
- Return a result that is either the same size as the group chunk
- Operate column-by-column on the group chunk
- Not perform in-place operations on the group chunk.
Now we perform some group-specific computations and return a like-indexed.
Filtration is a process in which we discard some groups, according to a group-wise computation that evaluates True or False. In order to filter a group, we use
filter method and apply some condition by which we filter group.
Now we filter data that to return the Name which have lived two or more times .
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