Adding in missing months to a dataframe with null values

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I have a DataFrame that I am trying to find the frequency of certain events with. So for example, it is listed as follows

Month Year Event UniqueID
1     2018 A     01
1     2018 A     02
2     2018 B     03
....

etc. I have everything grouped by frequency of Event per year. I did that by using the following code.

This counts up all the events so I can average them

df.groupby(['Year','Month','Event'])['Event'].size().rename('Count of Events').reset_index()

Which gives us something along the lines of

Year Month Event Count of Events
2018 01    A     2
2018 02    B     1
...

And then I'm getting the average of how often it happens a month for the entire year by using

df.groupby(['Event'])['Count of Events'].mean()

Which gives me the average. However one thing I noticed is that I may have gaps. For example event 'A', may occur in Jan and Feb, but not March, so this won't give me a true "average" over the year. What would be the best way to "Plug up" These holes? For example, in the above example list,

Month Year Event Count of Events
1     2018 A     02
1     2018 B     00
1     2018 C     00
2     2018 A     00
2     2018 B     00
2     2018 B     01
...

Would be the optimal final outcome before I average it. Thank you!

You were close to the solution. After grouping, unstack the dataframe to a "wide" form (that way you will have every combination of a month and a year), fill the missing values with 0s, and stack it back:

df.groupby(["Month", "Year", "Event"]).size().unstack().fillna(0).stack()
#Month  Year  Event
#1      2018  A        2.0
#             B        0.0
#2      2018  A        0.0
#             B        1.0

Working with Missing Data in Pandas, Campus Ambassador Program � Geek of the Month � Placement Course � Project � Competitive Programming Missing Data can also refer to as NA (Not Available) values in pandas. In order to check null values in Pandas DataFrame, we use isnull() function this function return creating bool series True for NaN values. I have a pandas dataframe that is used to create a JSON which in turn is used to display a highcharts chart. Pandas dataframe: Date colA colB 12-Sep-14 20 40 13-Sep-14 50 10 14-Sep-14 12 -20 15-Sep-14 74 43 Is there a way to change some of the colA and colB values to null.

Python, fill_value : [None or float value, default None] Fill missing (NaN) values with this value. If both DataFrame locations are missing, the result will be missing. level : [ int� Filling missing values using fillna (), replace () and interpolate () In order to fill null values in a datasets, we use fillna (), replace () and interpolate () function these function replace NaN values with some value of their own. All these function help in filling a null values in datasets of a DataFrame.

I think what you need is fillna: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.fillna.html

It's a really easy way to fill null values and designate what to fill them with.

Working with missing data — pandas 1.0.5 documentation, While NaN is the default missing value marker for reasons of computational speed You can insert missing values by simply assigning to containers. in numpy ; previously sum/prod of all-NA or empty Series/DataFrames would return NaN. It will return a boolean series, where True for not null and False for null values or missing values. >df.Last_Name.notnull() 0 True 1 False 2 True Name: Last_Name, dtype: bool We can use this boolean series to filter the dataframe so that it keeps the rows with no missing data for the column ‘Last_Name’.

Working with missing data — pandas 0.12.0 documentation, of financial time series, some of the time series might start on different dates. While NaN is the default missing value marker for reasons of computational speed h NaN -1.679253 -1.636722 In [20]: df['one'].sum() 0.51468201281996417 In -1.636722 In [31]: df.dropna(axis=0) Empty DataFrame Columns: [one, two,� Fill Missing Values within Each Group. This is when the group_by command from the dplyr package comes in handy. We can add ‘Group By’ step to group the data by Product values (A or B) before running ‘fill’ command operation. In R, you can write the script like below.

Cleaning Missing Values in a Pandas Dataframe, pandas series denoting features and the sum of their null values If there are no missing values, then it will just output an empty dataframe. Here, we either delete a particular row if it has a null value for a particular feature and a particular column if it has more than 70-75% of missing values. This method is advised only when there are enough samples in the data set. One has to make sure that after we have deleted the data, there is no addition of bias.

How to fill in arbitrary missing dates in Pandas dataframe?, Pandas filling missing dates and values within group, Initial Dataframe: dt user val 0 Here is the code to create the data frame. i want to add the The fillna function can “fill in” NA values with non-null data in a couple of ways, which we � Sometimes csv file has null values, which are later displayed as NaN in Data Frame. Just like pandas dropna() method manage and remove Null values from a data frame, fillna() manages and let the user replace NaN values with some value of their own.

Comments
  • Awesome! Thank you so much! Is there an easy way to keep the 4th column (The "derived" count of column named this way without using .rename?
  • I think the issue is that some combinations of the groupby columns (Year, Month) simply don't appear in the original DataFrame, so the resulting DataFrame is missing entire rows -- there are no np.nan values to fill at all.