删除还是填充：明智选择

When you meet missing data, you face one big choice: drop the affected rows, or fill them in. The right road depends on how much you lose either way. 🛣️

The method dropna() removes any row that has at least one missing value. It is clean and simple, but it can quietly delete a lot of data.

If one column is mostly empty, drop the whole column with axis=1. Sometimes a single bad column hurts more than the rows it sits in.

Dropping works well when gaps are rare and scattered. Losing a tiny fraction of a large dataset rarely changes your conclusions.

If many rows share even one gap, dropping can shrink your data drastically. Worse, the rows you lose may not be random, which biases results.

The alternative is to fill missing cells with a sensible value using fillna(). You keep every row, at the cost of inventing some numbers.

Remember that every filled value is an estimate. A good fill is reasonable and documented; a careless one hides the gap and warps your stats.

You can keep rows that have enough real data using thresh, which sets the minimum number of non-missing values a row must have to survive.

Use subset to drop rows only when a specific key column is missing. This protects the rest of your data from unnecessary deletion.

Before deciding, ask why the value is absent. Data missing at random is safe to fill, but a systematic gap may itself be a meaningful signal.

A handy guide: drop when gaps are few, fill when rows are precious. Always weigh how each choice reshapes your distribution before committing.

A column is 80% empty but every row has useful data elsewhere. What is usually the wisest move?

You now weigh drop versus fill by how much data you lose and why values are missing. Use dropna, thresh, and subset to delete with care.