从python中的pandas Series和DataFrames获取字符串？
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getting string from pandas Series and DataFrames in python?
提问by
I have this dataframe in pandas:
我在熊猫中有这个数据框：
d=pandas.DataFrame([{"a": 1, "b": 1}, {"c": 2, "b": 4}])
d["name"] = ["Hello", "World"]
I want to select an element based on its string value in "name" column and then get the value as a string. To select the element:
我想根据“名称”列中的字符串值选择一个元素，然后将值作为字符串获取。要选择元素：
d[d["name"] == "World"]["name"]
Out:
1 World
Name: name
The problem is that it doesn't give a simple string but a series. Casting to a string won't help -- how can I just get the string "World"out of this? Is this the only way?
问题是它没有给出一个简单的字符串，而是一个系列。投射到字符串无济于事——我怎么能把字符串从中取"World"出来呢？这是唯一的方法吗？
d[d["name"] == "World"]["name"].values[0]
thanks.
谢谢。
采纳答案by Andy Hayden
As @DSM points out, in general there could be many rows with name 'World', so somewhere down the line we'll need to pick one.
正如@DSM 指出的那样，通常可能有很多行带有 name 'World'，所以我们需要在某处选择一个。
One way to do this which seems kind of nice could be to use where(and then max):
一种看起来不错的方法是使用where（然后使用max）：
In [11]: d.name.where(d.name == 'World', np.nan)
Out[11]:
0 NaN
1 World
Name: name, dtype: object
In [12]: d.name.where(d.name == 'World', np.nan).max()
Out[12]: 'World'
Note: if there is no row with name 'World' this will return NaN.
注意：如果没有名称为“World”的行，这将返回 NaN。
回答by Blairg23
There's one method that no one mentioned that might be worth noting. This was a problem I was having where I was doing multiple criteria checks and getting back a single item Series (basically a unique row result). If you have a single item in a Series and just need that item OR know the index of the particular item you want to gather, just do this:
有一种没有人提到的方法可能值得注意。这是我在进行多项标准检查并取回单个项目系列（基本上是唯一的行结果）时遇到的问题。如果您在系列中有一个项目并且只需要该项目或知道您要收集的特定项目的索引，请执行以下操作：
d[d["name"] == "World"].tolist()[0]
for the first (and only) item in a single item Series.
对于单个项目系列中的第一个（也是唯一一个）项目。
Or this:
或这个：
d[d["name"] == "World"].tolist()[index]
where indexis the index of the item you are looking for in the Series.
index您在系列中查找的项目的索引在哪里。
If you want it as a string, you may have to cast as a string if it is not already stringified by default.
如果您希望将其作为字符串，并且默认情况下尚未将其字符串化，则可能必须将其转换为字符串。
回答by blissweb
Not sure what versions of Pandas this works in, but its one other option:
不确定这适用于哪些版本的 Pandas，但它是另一种选择：
d[d["name"] == "World"].to_string(index=False)
and if more than one row there are other options:
如果不止一行，还有其他选项：
max_rows int, optional
Maximum number of rows to show before truncating. If None, show all.
截断前显示的最大行数。如果没有，则显示全部。
min_rows int, optional
The number of rows to display in a truncated repr (when number of rows is above max_rows).
在截断的 repr 中显示的行数（当行数高于 max_rows 时）。
