Como você lida com valores ausentes ao preparar dados para aprendizado de máquina?

Identifying the missing values in your dataset is very crucial, understanding the extent of the missing values and how they are dispersed. Then Imputation, replacing missing values with a statistical measure like mean, median or mode.

The first step is understanding the extent and distribution of missing data. Tools like pandas in Python offer functions like isna() and isnull() to identify missing values in your dataset. Visualizing missing data patterns using heatmaps and bar charts can reveal insights into the nature of missingness.

In my experience,when the missing values depends on the missing variable itself, it has a great impact on the data analysis and it is also necessary to check the selected methods for the management more carefully.

Imputation refers to filling in missing values with plausible estimates. Popular methods include: Mean/Median Imputation: Replacing missing values with the mean or median of the respective feature. Mode Imputation: Filling missing values with the mode (most frequent value) of the feature. K-Nearest Neighbors (KNN): Using the average of K nearest neighbors with known values for the missing value. Model-Based Imputation: Training a separate model, like a regression or decision tree, to predict missing values based on other features.

Dropping rows or columns with missing values is a straightforward approach, but it can lead to data loss, especially if missingness is extensive. This method is best suited when missing data is minimal or randomly distributed and unlikely to introduce bias.

For example,if the missing values are related to variables that do not affect the analysis or at least do not have a direct effect,it may be acceptable to drop them.

In some cases, ignoring missing data altogether ("listwise deletion") might be appropriate. This approach preserves the original data distribution but can be statistically inefficient. Alternatively, weighting instances based on the proportion of missing values can adjust for the bias introduced by missingness.

Creating new features based on missingness patterns can sometimes be beneficial. For example, you can generate a binary feature indicating whether a value is missing or not. This approach can capture the underlying information associated with missing data.

Certain machine learning algorithms are more robust to missing values than others. For instance, decision trees handle missing data intrinsically, while linear regression might require specific imputation techniques. Choosing an algorithm suited to your missing data scenario can improve model performance.

Missing Data Mechanism: Understanding the reason behind missing values (MCAR, MAR, MNAR) can guide your imputation strategy. Domain Knowledge: Incorporating domain expertise can help choose appropriate imputation values or guide feature engineering. Evaluation: Continuously evaluating the impact of your missing value handling approach on model performance is crucial.