如何使用Python中另一列中的选定值添加新列

Question

我一整天都在想办法解决这个问题。我是Python新手。在

我有一张大约有50000张唱片的桌子。但下表将解释我要做什么。在

我想添加第三列，名为Category。此列将包含“电影”列上设置的基于值的结果。在

-----------------------------------------
N     | Movies               
-----------------------------------------
1        | Save the Last Dance 
-----------------------------------------
2        | Love and Other Drugs
---------------------------------------
3        | Dance with Me      
---------------------------------------
4        | Love Actually       
---------------------------------------
5        | High School Musical
----------------------------------------

条件是这样的；在Movies列中搜索这些单词{舞蹈、爱情和音乐）。如果在字符串中找到该单词，请在“类别”列中返回该单词。在

这将在最后产生一个类似这样的新数据帧

^{pr2}$

提前谢谢！！在

Answer 1

一种更快的方法是为所有类别创建一个遮罩，假设您的数字很小：

In [22]:

dance_mask = df['Movies'].str.contains('Dance')
love_mask = df['Movies'].str.contains('Love')
musical_mask = df['Movies'].str.contains('Musical')
df[dance_mask]
Out[22]:
   N               Movies
0  1  Save the Last Dance
2  3        Dance with Me

[2 rows x 2 columns]

In [26]:
# now set category
df.ix[dance_mask,'Category'] = 'Dance'
df
Out[26]:
   N                Movies Category
0  1   Save the Last Dance    Dance
1  2  Love and Other Drugs      NaN
2  3         Dance with Me    Dance
3  4         Love Actually      NaN
4  5   High School Musical      NaN

[5 rows x 3 columns]

In [28]:
# repeat for remaining masks
df.ix[love_mask,'Category'] = 'Love'
df.ix[musical_mask,'Category'] = 'Musical'
df
Out[28]:
   N                Movies Category
0  1   Save the Last Dance    Dance
1  2  Love and Other Drugs     Love
2  3         Dance with Me    Dance
3  4         Love Actually     Love
4  5   High School Musical  Musical

[5 rows x 3 columns]

Answer 2

如果你有一个二维列表，那么就这样做：

def add_category(record):
    movie = record[1]
    categories = []
    for category in ['Dance', 'Love', 'Musical']:
        if category in movie:
            categories.append(category)
    return record.append(', '.join(categories))

database = [add_category(record) for record in database]

您可以通过更改add_category()函数来更改category列值的计算方式。在