How do you handle missing data in pandas effectively?

You will encounter nulls in almost every data available to you but how you handle it depends on your understanding of the problem and reason of that null present. If it represents a specific value for example 0 (in case of no sales in a store), you can use fillna(0). on the other hand if it means data wasn't captured and we aren't sure of the value its best to drop or impute the value.

You can try to sum the nulls first to know the percentage of the null data, so you can identify if it's a real problem in your dataset or not. Therefore, you can find the right strategy to deal with it.

It is important to know how "dropna()" might affect your datasets, particularly if your are incorporating this to a workflow. For example, merges are notorious for creating many NAs so one most proceed with caution and be thoughtful about the changes this could cause. Always keep an original dataset as backup, just in case.

After checking the percentage of missing data, it's a common practice to remove them if it's less than 5%. However, that decision depends on many other factors such as dataset size and the sensitivity of the data.

These methods are considered basic ones; you can use them if the column is not in a time series and is not very crucial for predictions. If so, there are other methods that will be discussed in the next points.

In case you want to fill data as if it's in a time series, you can use interpolation. To understand it easily, it's something close to drawing a line that touches all points, and if there is a missing point, it's expected to be on that line.

This is a good idea, yet you need to understand the option you are applying, because more or less this will affect the output data you are working with. Also, check the documentation and experiment with small datasets to see how the algorithm handles missing data before applying it to your entire dataset.

I don't recommend the common category if there are a big percentage of NA, as it will change the output drastically. Maybe you can do that if there is a low percentage, or the category is not important in your analysis, or there is some kind of correlation between this category and other values.

Handling missing data in Pandas effectively involves several strategies: 1. Identify missing values: Use methods like `isnull()` or `notnull()` to identify missing data in your DataFrame. 2. Remove missing data: Use `dropna()` to remove rows or columns with missing values. Specify `axis` and `thresh` parameters for more control. 3. Imputation: Fill missing values using `fillna()` with strategies like mean, median, mode, or a specific value. 4. Interpolation: Use `interpolate()` to fill missing values based on linear or polynomial interpolation. 5. Forward or backward fill: Use `ffill()` or `bfill()` to fill missing values with the previous or next valid value, respectively.

6. Masking: Use boolean indexing to filter out rows or columns with missing values. 7. Advanced imputation techniques: Utilize libraries like scikit-learn or fancyimpute for more advanced imputation methods like KNN imputation or matrix factorization. 8. Domain-specific imputation: Use domain knowledge to fill missing values based on business rules or logical assumptions. 9. Considerations for time series: For time series data, use methods like `fillna(method='ffill')` or `interpolate()` with time-based strategies. 10. Visualize missing data: Use visualization libraries like matplotlib or seaborn to visualize missing data patterns and decide on the appropriate handling strategy.

There are some machine learning methods that you might find interesting, like KNN. Also, the ffill method. You can modify these methods if it's related to your knowledge, such as knowing there was a specific error that day in item X, so the missing values should be for that item. All of this should be according to the situation. There is no rule to fit everything.