need to fill the NA values with the past three values before na values in python

问题

need to fill the NA values with the past three values mean of that NA

this is my dataset

RECEIPT_MONTH_YEAR NET_SALES

0 2014-01-01 818817.20

1 2014-02-01 362377.20

2 2014-03-01 374644.60

3 2014-04-01 NA

4 2014-05-01 NA

5 2014-06-01 NA

6 2014-07-01 NA

7 2014-08-01 46382.50

8 2014-09-01 55933.70

9 2014-10-01 292303.40

10 2014-10-01 382928.60

回答1:

is this dataset a .csv file or a dataframe. This NA is a 'NaN' or a string ?

import pandas as pd
import numpy as np
df=pd.read_csv('your dataset',sep=' ')
df.replace('NA',np.nan)
df.fillna(method='ffill',inplace=True)

you mention something about mean of 3 values..the above simply forward fills the last observation before the NaNs begin. This is often a good way for forecasting (better than taking means in certain cases, if persistence is important)

 ind = df['NET_SALES'].index[df['NET_SALES'].apply(np.isnan)]
 Meanof3 = df.iloc[ind[0]-3:ind[0]].mean(axis=1,skipna=True)
 df.replace('NA',Meanof3)

Maybe the answer can be generalised and improved if more info about the dataset is known - like if you always want to take the mean of last 3 measurements before any NA. The above will allow you to check the indices that are NaNs and then take mean of 3 before, while ignoring any NaNs

回答2:

This is simple but it is working

df_data.fillna(0,inplace=True)
for i in range(0,len(df_data)):
if df_data['NET_SALES'][i]== 0.00:
    condtn = df_data['NET_SALES'][i-1]+df_data['NET_SALES'][i-2]+df_data['NET_SALES'][i-3]
    df_data['NET_SALES'][i]=condtn/3

回答3:

You could use fillna (assuming that your NA is already np.nan) and rolling mean:

import pandas as pd
import numpy as np

df = pd.DataFrame([818817.2,362377.2,374644.6,np.nan,np.nan,np.nan,np.nan,46382.5,55933.7,292303.4,382928.6], columns=["NET_SALES"])

df["NET_SALES"] = df["NET_SALES"].fillna(df["NET_SALES"].shift(1).rolling(3, min_periods=1).mean())

Out:

NET_SALES
0   818817.2
1   362377.2
2   374644.6
3   518613.0
4   368510.9
5   374644.6
6   NaN
7   46382.5
8   55933.7
9   292303.4
10  382928.6

If you want to include the imputed values I guess you'll need to use a loop.

来源：https://stackoverflow.com/questions/50151197/need-to-fill-the-na-values-with-the-past-three-values-before-na-values-in-python

标签

python-3.x

time-series

forecasting

fillna