如何从 pandas 数据框中获取单个值作为字符串 [英] How to get a single value as a string from pandas data frame

问题描述

我正在从数据框查询一个似乎是'dtype:object'的值.我只想按原样打印值，而不打印索引或其他信息.我该怎么做?

I am querying a single value from my data frame which seems to be 'dtype: object'. I simply want to print the value as it is with out printing the index or other information as well. How do I do this?

col_names = ['Host', 'Port']
df = pd.DataFrame(columns=col_names)
df.loc[len(df)] = ['a', 'b']

t = df[df['Host'] == 'a']['Port']
print(t)

输出:

预期输出: b

推荐答案

如果可以保证只返回一个结果，请使用loc并调用item:

If you can guarantee only one result is returned, use loc and call item:

>>> df.loc[df['Host'] == 'a', 'Port'].item()
'b'

或者类似地，

>>> df.loc[df['Host'] == 'a', 'Port'].values[0]
'b'

...以获取 first 值(类似地，第二个为.values[1]).哪个优于df.loc[df['Host'] == 'a', 'Port'][0]，因为如果您的DataFrame如下所示，

...to get the first value (similarly, .values[1] for the second). Which is better than df.loc[df['Host'] == 'a', 'Port'][0] because, if your DataFrame looks like this,

  Host Port
1    a    b

然后将引发"KeyError:0" —

Then "KeyError: 0" will be thrown—

df.loc[df['Host'] == 'a', 'Port'][0]
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)

---

或者，使用at:

>>> df.at[df['Host'].eq('a').idxmax(), 'Port']
'b'

缺点是如果'a'不存在，idxmax将返回第一个索引(并返回错误的结果).

The drawback is that if 'a' doesn't exist, idxmax will return the first index (and return an incorrect result).

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