kaggle练习题、pandas练习题(Exercise: Summary Functions and Maps)

Exercise: Summary Functions and Maps

1.What is the median of the points column in the reviews DataFrame?

median_points = reviews.points.median()

2.What countries are represented in the dataset? (Your answer should not include any duplicates.)

countries = reviews.country.unique()

3.How often does each country appear in the dataset? Create a Series reviews_per_country mapping countries to the count of reviews of wines from that country.

reviews_per_country = reviews['country'].value_counts()

4.Create variable centered_price containing a version of the price column with the mean price subtracted.(Note: this ‘centering’ transformation is a common preprocessing step before applying various machine learning algorithms.)

a = reviews.price.mean()
centered_price = reviews.price.map(lambda p: p - a)