str(x) 和 x.str 有什么区别？

Question

What I needed to happen:

Get all commas in a Pandas DataFrame replaced with dots.

What I tried to do:

df.apply(lambda x: str(x).replace(",", "."))

When I tried this, I got an error:

ValueError: Must have equal len keys and value when setting with an iterable.

What was the correct answer:

(found on StackOverflow)

df.apply(lambda x: x.str.replace(",", "."))

My question:

What is the difference between str(x) and x.str, and why only one of them worked?

Answer 1

pandas.Series.str (the.str.) gives you a series that it works on each column

pandas.DataFrame.apply works on columns or rows. by default row (axis{0 or 'index', 1 or 'columns'}, default 0).

The difference is that str(x) is operating on the index of the dataframe, as apply operates on the axis=0 by default, and the .str. is returning a series