我想要找到我的数据中每一列的
NaN
数量。import pandas as pd
import numpy as np
# example DataFrame
df = pd.DataFrame({'a':[1,2,np.nan], 'b':[np.nan,1,np.nan]})
# Check whether there are null values in columns
null_columns = df.columns[df.isnull().any()]
print(df[null_columns].isnull().sum())
# One can follow along further per the cited article
如果你需要通过groupby获取不是NA(非None)和NA(None)的计数,请按如下方式操作:
gdf = df.groupby(['ColumnToGroupBy'])
def countna(x):
return (x.isna()).sum()
gdf.agg(['count', countna, 'size'])
此函数返回每个组的非NA计数、NA计数和总条目数。
# check missing values
import numpy as np, pandas as pd
for col in df:
print(col +': '+ np.str(df[col].isna().sum()))
for col, val in df.iteritems():
if (df[col].isnull().sum() / len(val) * 100) > 30:
df.drop(columns=col, inplace=True)
根据给出的答案和一些改进,这是我的方法。
def PercentageMissin(Dataset):
"""this function will return the percentage of missing values in a dataset """
if isinstance(Dataset,pd.DataFrame):
adict={} #a dictionary conatin keys columns names and values percentage of missin value in the columns
for col in Dataset.columns:
adict[col]=(np.count_nonzero(Dataset[col].isnull())*100)/len(Dataset[col])
return pd.DataFrame(adict,index=['% of missing'],columns=adict.keys())
else:
raise TypeError("can only be used with panda dataframe")
df.apply(lambda x: x.value_counts(dropna=False)[np.nan]/x.size*100)
。 - K.-Michael Ayeimport pandas as pd
import numpy as np
# example DataFrame
df = pd.DataFrame({'a':[1,2,np.nan], 'b':[np.nan,1,np.nan]})
# count the NaNs in a column
num_nan_a = df.loc[ (pd.isna(df['a'])) , 'a' ].shape[0]
num_nan_b = df.loc[ (pd.isna(df['b'])) , 'b' ].shape[0]
# summarize the num_nan_b
print(df)
print(' ')
print(f"There are {num_nan_a} NaNs in column a")
print(f"There are {num_nan_b} NaNs in column b")
输出结果为:
a b
0 1.0 NaN
1 2.0 1.0
2 NaN NaN
There are 1 NaNs in column a
There are 2 NaNs in column b
np.count_nonzero
和 .isna():np.count_nonzero(df.isna())
%timeit np.count_nonzero(df.isna())
512 ms ± 24.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
与使用1000005行×16列数据框的顶级答案相比:
%timeit df.isna().sum()
492 ms ± 55.2 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
%timeit df.isnull().sum(axis = 0)
478 ms ± 34.9 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
%timeit count_nan = len(df) - df.count()
484 ms ± 47.4 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
数据:
raw_data = {'first_name': ['Jason', np.nan, 'Tina', 'Jake', 'Amy'],
'last_name': ['Miller', np.nan, np.nan, 'Milner', 'Cooze'],
'age': [22, np.nan, 23, 24, 25],
'sex': ['m', np.nan, 'f', 'm', 'f'],
'Test1_Score': [4, np.nan, 0, 0, 0],
'Test2_Score': [25, np.nan, np.nan, 0, 0]}
results = pd.DataFrame(raw_data, columns = ['first_name', 'last_name', 'age', 'sex', 'Test1_Score', 'Test2_Score'])
# big dataframe for %timeit
big_df = pd.DataFrame(np.random.randint(0, 100, size=(1000000, 10)), columns=list('ABCDEFGHIJ'))
df = pd.concat([big_df,results]) # 1000005 rows × 16 columns
df1 = pd.DataFrame({'a':[1,2,np.nan], 'b':[np.nan,1,np.nan]})
def info_as_df (df):
null_counts = df.isna().sum()
info_df = pd.DataFrame(list(zip(null_counts.index,null_counts.values))\
, columns = ['Column', 'Nulls_Count'])
data_types = df.dtypes
info_df['Dtype'] = data_types.values
return info_df
print(df1.info())
print(info_as_df(df1))
这将会给出:
<class 'pandas.core.frame.DataFrame'>
RangeIndex: 3 entries, 0 to 2
Data columns (total 2 columns):
# Column Non-Null Count Dtype
--- ------ -------------- -----
0 a 2 non-null float64
1 b 1 non-null float64
dtypes: float64(2)
memory usage: 176.0 bytes
None
Column Nulls_Count Dtype
0 a 1 float64
1 b 2 float64
#import the dataframe
import pandas as pd
reviews = pd.read_csv("../input/wine-reviews/winemag-data-130k-v2.csv", index_col=0)
要获取缺失的值,使用变量n_missing_prices,只需执行以下操作
n_missing_prices = sum(reviews.price.isnull())
print(n_missing_prices)
这里的关键方法是sum,之前尝试使用count,但意识到在这种情况下使用sum才是正确的方法。
在我的代码中使用了@sushmit提出的解决方案。
同样的,还有可能有一种变化。
colNullCnt = []
for z in range(len(df1.cols)):
colNullCnt.append([df1.cols[z], sum(pd.isnull(trainPd[df1.cols[z]]))])
这样做的优点是,它会返回数据框中每列的结果。
df.info()
不会返回一个DataFrame,该方法只是打印信息。 - jorisdf.info()
即可提供每列的数据类型和非空计数。 - Rishabh