在不使用索引的情况下替换pandas DataFrame中选定单元格的值 [英] Replace value for a selected cell in pandas DataFrame without using index
问题描述
这是与此问题,但有一个主要区别:我选择的数据不是按其索引而是按某些条件进行更改.
this is a rather similar question to this question but with one key difference: I'm selecting the data I want to change not by its index but by some criteria.
如果我应用的条件返回一行,我希望能够以一种简单的方式设置该行中某个列的值,但是我的第一次尝试不起作用:
If the criteria I apply return a single row, I'd expect to be able to set the value of a certain column in that row in an easy way, but my first attempt doesn't work:
>>> d = pd.DataFrame({'year':[2008,2008,2008,2008,2009,2009,2009,2009],
... 'flavour':['strawberry','strawberry','banana','banana',
... 'strawberry','strawberry','banana','banana'],
... 'day':['sat','sun','sat','sun','sat','sun','sat','sun'],
... 'sales':[10,12,22,23,11,13,23,24]})
>>> d
day flavour sales year
0 sat strawberry 10 2008
1 sun strawberry 12 2008
2 sat banana 22 2008
3 sun banana 23 2008
4 sat strawberry 11 2009
5 sun strawberry 13 2009
6 sat banana 23 2009
7 sun banana 24 2009
>>> d[d.sales==24]
day flavour sales year
7 sun banana 24 2009
>>> d[d.sales==24].sales = 100
>>> d
day flavour sales year
0 sat strawberry 10 2008
1 sun strawberry 12 2008
2 sat banana 22 2008
3 sun banana 23 2008
4 sat strawberry 11 2009
5 sun strawberry 13 2009
6 sat banana 23 2009
7 sun banana 24 2009
因此,与其将2009年周日的香蕉销量设置为100,就什么都没有发生!最好的方法是什么?理想情况下,解决方案应该使用行号,因为您通常不事先知道!
So rather than setting 2009 Sunday's Banana sales to 100, nothing happens! What's the nicest way to do this? Ideally the solution should use the row number, as you normally don't know that in advance!
推荐答案
多种方法
In [7]: d.sales[d.sales==24] = 100
In [8]: d
Out[8]:
day flavour sales year
0 sat strawberry 10 2008
1 sun strawberry 12 2008
2 sat banana 22 2008
3 sun banana 23 2008
4 sat strawberry 11 2009
5 sun strawberry 13 2009
6 sat banana 23 2009
7 sun banana 100 2009
2
In [26]: d.loc[d.sales == 12, 'sales'] = 99
In [27]: d
Out[27]:
day flavour sales year
0 sat strawberry 10 2008
1 sun strawberry 99 2008
2 sat banana 22 2008
3 sun banana 23 2008
4 sat strawberry 11 2009
5 sun strawberry 13 2009
6 sat banana 23 2009
7 sun banana 100 2009
3
In [28]: d.sales = d.sales.replace(23, 24)
In [29]: d
Out[29]:
day flavour sales year
0 sat strawberry 10 2008
1 sun strawberry 99 2008
2 sat banana 22 2008
3 sun banana 24 2008
4 sat strawberry 11 2009
5 sun strawberry 13 2009
6 sat banana 24 2009
7 sun banana 100 2009
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