Blog
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Pandas groupby on datetime parts with the dt accessor
If your Python Pandas data frame has a datetime column, you can group on a portion of that via the “dt” accessor. For example, let’s get mean trip_distance for each hour of the day:
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Pandas groupby: Aggregating multiple columns with multiple functions
Does Python Pandas allow multiple data columns and multiple methods? Yes! The above returns a data frame. Its 4 columns are a 2-level multi-index with mean/std in the inner level.
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Pandas groupby: Multiple columns and multiple aggregation methods
Does Python Pandas allow multiple categorical columns and multiple methods? Yes! The above returns: – A 2-column data frame (mean + std)– A 2-level index (passenger_count + VendorID)
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Pandas groupby: Get a data frame instead of a series
groupby on a single column in Python Pandas returns a series. Want a single-column data frame? Instead of pass a one-element list of data columns:
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Pandas groupby with two columns: Reshape results with unstack
Invoke “groupby” with two categorical columns in Python Pandas, and get a two-part multi-index: Turn into a data frame with unstack:
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Pandas groupby with sort=False: Keep groups in order of appearance
A “groupby” call in Python Pandas is normally sorted by index. But if you’re grouping by month name, April will come before January. Pass “sort=False”, and the index will reflect the order of appearance:
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Pandas groupby basics: Aggregating a numeric column by category
The simplest grouping in Python Pandas is groupby: For example: Returns a series whose index is the unique values from passenger_count.
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Pandas dropna with thresh: Drop only rows with too many NaN values
You can remove NaN from a Python Pandas data frame with dropna, but be careful: It removes rows with even one NaN, which can be overkill. Pass “thresh” to allow some rows to remain, even if they contain NaN:
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Pandas dropna: The best way to remove NaN values from a series
Coming to Python Pandas from NumPy? You’ll reach for np.isnan: Unfortunately, this works. Better, use s.isna (or s.isnull). But the best way to drop NaN? Use dropna:
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New on the LernerPython practice system: A visual debugger
I’m a big fan of exercises, which is why the LernerPython platform includes hundreds of them — all using my in-browser practice system, which handles Python, Pandas, and Git, along with an AI-based Socratic tutor based on my writing. As of today, the practice system is even better: It includes a visual debugger, allowing you…