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[英]Most efficient way to loop through and update rows in a large pandas dataframe
[英]Fast, efficient way to remove rows from large Pandas DataFrame
我希望从大型Pandas DataFrame中删除行,其中包含基于用户在网站上执行的操作/事件的分析数据。 所有用户操作流都以start
事件start
,并以end
事件end
。 我想查找已完成特定事件的所有用户(例如signed up
- 示例数据框中的索引13)并删除该事件之后的所有事件,直到(并包括) end
事件。 因此,在此示例中,必须从数据框中删除已viewed blog post
, page view
, visited site
, ad campaign hit
,已viewed blog post
, visited site
, page view
和end
。
In [26]: data
Out[26]:
event user
0 start user1
1 visited blog user1
2 page view user1
3 visited blog user1
4 viewed blog post user1
5 ad campaign hit user1
6 page view user1
7 visited site user1
8 visited blog user1
9 viewed blog post user1
10 visited site user1
11 page view user1
12 signed up user1
13 viewed blog post user1
14 page view user1
15 visited site user1
16 ad campaign hit user1
17 viewed blog post user1
18 visited site user1
19 page view user1
20 end user1
我尝试过多种方式 - 使用np.where()
来识别正确的行或
removal_starts_at = data[(data.user == 'user1') & (data.event == 'signed up')]
removal_ends_at = data[(data.user == 'user1') & (data.event == 'end')]
data[data.user == 'user1'].drop(data.index[removal_start_at+1:removal_ends_at+1], inplace=True)
但是,这真的很慢! 每个用户需要大约20秒。 我有1000个用户,所以效率不高。 如果可能的话,我想要以更快的方式做到这一点。
我在撰写这个问题时发现的另一个问题是:如果我不将[data.user == 'user1']
包含在数据[data.user == 'user1']
子集中,它会变得疯狂并占用计算机上的所有内存。 如果我确实包含它,它实际上不会进行子集化并给我一个关于SettingWithCopy
的警告。
我对Pandas比较陌生,所以很可能有一种更简单的方法可以做到这一点而且我只是完全错误地做了。 我想过的想法是使用MultiIndex
直接找到用户和事件的组合,或者以更有效的方式进行子集化?
如果我理解正确,那么你的想法就是在一个数据框中有很多用户。 所以我把它扩展为有2个用户。 如果这是对的,那么这样的事情应该很快:
df['keep'] = np.where( df['event'] == 'start', 1, np.nan )
df['keep'] = np.where( df['event'].shift() == 'signed up', 0, df['keep'] )
df['keep'] = df['keep'].ffill()
event user keep
0 start user1 1
1 visited blog user1 1
2 page view user1 1
3 signed up user1 1
4 viewed blog post user1 0
5 page view user1 0
6 end user1 0
7 start user2 1
8 visited blog user2 1
9 signed up user2 1
10 viewed blog post user2 0
11 end user2 0
df[df['keep']==1]
event user keep
0 start user1 1
1 visited blog user1 1
2 page view user1 1
3 signed up user1 1
7 start user2 1
8 visited blog user2 1
9 signed up user2 1
我只是存储我想要的索引,然后从那里使用一个切片。
In [15]: idx = data.query('user=="user1" and event=="signed up"').index[0]
In [16]: data[:idx+1]
Out[16]:
event user
0 start user1
1 visited blog user1
2 page view user1
3 visited blog user1
4 viewed blog post user1
5 ad campaign hit user1
6 page view user1
7 visited site user1
8 visited blog user1
9 viewed blog post user1
10 visited site user1
11 page view user1
12 signed up user1
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