pandas dropna()函数不起作用 [英] Pandas dropna() function not working
问题描述
我正在尝试从熊猫数据框中删除NA值.
I am trying to drop NA values from a pandas dataframe.
我用过dropna()(它应该删除数据帧中的所有NA行).但是，它不起作用.
I have used dropna() (which should drop all NA rows from the dataframe). Yet, it does not work.
这是代码:
import pandas as pd
import numpy as np
prison_data = pd.read_csv('https://andrewshinsuke.me/docs/compas-scores-two-years.csv')
这就是获取数据框的方式.如下所示，默认的read_csv方法确实将NA数据点转换为np.nan.
That's how you get the data frame. As the following shows, the default read_csv method does indeed convert the NA data points to np.nan.
np.isnan(prison_data.head()['out_custody'][4])
Out[2]: True
方便地，DF的head()已经包含一个NaN值(在out_custody列中)，因此打印prison_data.head()这样，您将得到:
Conveniently, the head() of the DF already contains a NaN values (in the column out_custody), so printing prison_data.head() this, you get:
id name first last compas_screening_date sex
0 1 miguel hernandez miguel hernandez 2013-08-14 Male
1 3 kevon dixon kevon dixon 2013-01-27 Male
2 4 ed philo ed philo 2013-04-14 Male
3 5 marcu brown marcu brown 2013-01-13 Male
4 6 bouthy pierrelouis bouthy pierrelouis 2013-03-26 Male
dob age age_cat race ...
0 1947-04-18 69 Greater than 45 Other ...
1 1982-01-22 34 25 - 45 African-American ...
2 1991-05-14 24 Less than 25 African-American ...
3 1993-01-21 23 Less than 25 African-American ...
4 1973-01-22 43 25 - 45 Other ...
v_decile_score v_score_text v_screening_date in_custody out_custody
0 1 Low 2013-08-14 2014-07-07 2014-07-14
1 1 Low 2013-01-27 2013-01-26 2013-02-05
2 3 Low 2013-04-14 2013-06-16 2013-06-16
3 6 Medium 2013-01-13 NaN NaN
4 1 Low 2013-03-26 NaN NaN
priors_count.1 start end event two_year_recid
0 0 0 327 0 0
1 0 9 159 1 1
2 4 0 63 0 1
3 1 0 1174 0 0
4 2 0 1102 0 0
但是，运行prison_data.dropna()不会以任何方式更改数据框.
However, running prison_data.dropna() does not change the dataframe in any way.
prison_data.dropna()
np.isnan(prison_data.head()['out_custody'][4])
Out[3]: True
默认情况下，
推荐答案
df.dropna()返回不包含NaN值的新数据集.因此，您必须将其分配给变量
df.dropna() by default returns a new dataset without NaN values. So, you have to assign it to the variable
df = df.dropna()
如果要其修改df就位，则必须显式指定
if you want it to modify the df inplace, you have to explicitly specify
df.dropna(inplace= True)
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