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problem description

Recently ~ found that the operation of elements in series is quite complex, for loop + Series.iloc[i] will occur stuck situation, then lambda is the solution:

error 1

ratings['timestamp'] = ratings['timestamp'].apply(ratings['timestamp'].iloc[i].strftime("%Y-%m-%d %H:%M:%S", ts) for i in range(len(ratings)))TypeError: 'generator' object is not callable

Applying lambda directly is equivalent to applying each element of each line one by one:

ratings_sub['timestamp'] = ratings_sub['timestamp'].apply(lambda x:time.strftime('%Y/%m/%d',time.localtime(x)))

Supplement: DataFrame and Series numerical operations

Principle 1:

The result of the operation returns the index of all occurrences

Principle 2:

Identical index addition

Principle 3:

Any value doing arithmetic with nan results in nan

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