python - Filtering Pandas DataFrames on dates

Question

I have a Pandas DataFrame with a 'date' column. Now I need to filter out all rows in the DataFrame that have dates outside of the next two months. Essentially, I only need to retain the rows that are within the next two months.

What is the best way to achieve this?

Answer 1

If date column is the index, then use .loc for label based indexing or .iloc for positional indexing.

For example:

df.loc['2014-01-01':'2014-02-01']

See details here http://pandas.pydata.org/pandas-docs/stable/dsintro.html#indexing-selection

If the column is not the index you have two choices:

1. Make it the index (either temporarily or permanently if it's time-series data)
2. df[(df['date'] > '2013-01-01') & (df['date'] < '2013-02-01')]

See here for the general explanation

Note: .ix is deprecated.

Answer 2

Previous answer is not correct in my experience, you can't pass it a simple string, needs to be a datetime object. So:

import datetime 
df.loc[datetime.date(year=2014,month=1,day=1):datetime.date(year=2014,month=2,day=1)]

Answer 3

And if your dates are standardized by importing datetime package, you can simply use:

df[(df['date']>datetime.date(2016,1,1)) & (df['date']<datetime.date(2016,3,1))]  

For standarding your date string using datetime package, you can use this function:

import datetime
datetime.datetime.strptime

Answer 4

If your datetime column have the Pandas datetime type (e.g. datetime64[ns]), for proper filtering you need the pd.Timestamp object, for example:

from datetime import date

import pandas as pd

value_to_check = pd.Timestamp(date.today().year, 1, 1)
filter_mask = df['date_column'] < value_to_check
filtered_df = df[filter_mask]

Answer 5

If you have already converted the string to a date format using pd.to_datetime you can just use:

df = df[(df['Date']> "2018-01-01") & (df['Date']< "2019-07-01")]

Answer 6

If the dates are in the index then simply:

df['20160101':'20160301']

Answer 7

You can use pd.Timestamp to perform a query and a local reference

import pandas as pd
import numpy as np

df = pd.DataFrame()
ts = pd.Timestamp

df['date'] = np.array(np.arange(10) + datetime.now().timestamp(), dtype='M8[s]')

print(df)
print(df.query('date > @ts("20190515T071320")')

with the output

                 date
0 2019-05-15 07:13:16
1 2019-05-15 07:13:17
2 2019-05-15 07:13:18
3 2019-05-15 07:13:19
4 2019-05-15 07:13:20
5 2019-05-15 07:13:21
6 2019-05-15 07:13:22
7 2019-05-15 07:13:23
8 2019-05-15 07:13:24
9 2019-05-15 07:13:25


                 date
5 2019-05-15 07:13:21
6 2019-05-15 07:13:22
7 2019-05-15 07:13:23
8 2019-05-15 07:13:24
9 2019-05-15 07:13:25

Have a look at the pandas documentation for DataFrame.query, specifically the mention about the local variabile referenced udsing @ prefix. In this case we reference pd.Timestamp using the local alias ts to be able to supply a timestamp string

Answer 8

The shortest way to filter your dataframe by date: Lets suppose your date column is type of datetime64[ns]

# filter by single day
df_filtered = df[df['date'].dt.strftime('%Y-%m-%d') == '2014-01-01']

# filter by single month
df_filtered = df[df['date'].dt.strftime('%Y-%m') == '2014-01']

# filter by single year
df_filtered = df[df['date'].dt.strftime('%Y') == '2014']

Answer 9

So when loading the csv data file, we'll need to set the date column as index now as below, in order to filter data based on a range of dates. This was not needed for the now deprecated method: pd.DataFrame.from_csv().

If you just want to show the data for two months from Jan to Feb, e.g. 2020-01-01 to 2020-02-29, you can do so:

import pandas as pd
mydata = pd.read_csv('mydata.csv',index_col='date') # or its index number, e.g. index_col=[0]
mydata['2020-01-01':'2020-02-29'] # will pull all the columns
#if just need one column, e.g. Cost, can be done:
mydata['2020-01-01':'2020-02-29','Cost'] 

This has been tested working for Python 3.7. Hope you will find this useful.

Answer 10

How about using pyjanitor

It has cool features.

After pip install pyjanitor

import janitor

df_filtered = df.filter_date(your_date_column_name, start_date, end_date)

Answer 11

I'm not allowed to write any comments yet, so I'll write an answer, if somebody will read all of them and reach this one.

If the index of the dataset is a datetime and you want to filter that just by (for example) months, you can do following:

df.loc[df.index.month == 3]

That will filter the dataset for you by March.

Answer 12

You could just select the time range by doing: df.loc['start_date':'end_date']