## How to Calculate change between rows in Pandas Data Frame

Suppose I have a daily sales record column. And from it I want to create two new columns. That keep track of the change from a month a go. For each day on the record. How would I go about doing this in Pandas Data frame. new to pandas and stuck here. here is a sample data set

And what I am looking for is to create a new column "Change from a month ago", which will tracks the difference between in daily sales between today and 30 days ago.

you can use pandas.DataFrame.diff

df['new_col'] = df.sales.diff(periods=30)

this will find the difference of current row and 30 rows above (this may or may not be 30 days ago)

**How to Calculate change between rows in Pandas Data Frame ,** Calculates the difference of a Dataframe element compared with another element in the Dataframe (default is element in previous row). Parameters. periodsint, default 1. Periods to shift for calculating difference, accepts negative values. Use the T attribute or the transpose() method to swap (= transpose) the rows and columns of pandas.DataFrame.Neither method changes the original object, but returns a new object with the rows and columns swapped (= transposed object).Note that depending on the data type dtype of each column, a view

**pandas.DataFrame.diff — pandas 1.1.1 documentation,** Computes the percentage change from the immediately previous row by default. This is useful Compute the difference of two elements in a DataFrame. Series. Overview: Difference between rows or columns of a pandas DataFrame object is found using the diff () method. The axis parameter decides whether difference to be calculated is between rows or between columns. When the periods parameter assumes positive values, difference is found by subtracting the previous row from the next row. When the periods parameter is negative difference is found by subtracting the next row from the previous row.

Getting a sense of the data you're using would certainly make it a lot easier to answer this. However, a common way to do it is by creating a new column in pandas using the `Series.shift`

operation in the following way:

import pandas as pd df = pd.DataFrame({'Col1': [10, 20, 15, 30, 45], 'Col2': [13, 23, 18, 33, 48], 'Col3': [17, 27, 22, 37, 52]}) df['Col4'] = df.Col1.shift(periods=-3) # reference df.Col1 value from 3 rows back

You can use this new column to do any arithmetic/algorithmic computation hereon.

**pandas.DataFrame.pct_change — pandas 1.1.1 documentation,** The first row will be NaN since that is the first value for column A, B and C. The percentage change between columns is calculated using the� The correlation between 1st and second row is 1 not 0.5. Correlation is a measure of linear relationship between variables. Here the two lists are strongly correlated with pearson's coefficient 1. If you plot row0 [2,6,8,12] against row1 [1,3,4,6] they all lie on a single line. Mean while if you want to find correlation between rows this should

**How to find Percentage Change in pandas,** You can refer the following code which calculates the difference between the rows: In [26]: data. Out[26]:. Date Close Adj Close. The pct_change() method of DataFrame class in pandas computes the percentage change between the rows of data. Note that, the pct_change() method calculates the percentage change only between the rows of data and not between the columns. Whereas, the diff() method of Pandas allows to find out the difference between either columns or rows.

**Calculating the difference between two rows in Python / Pandas ,** pandas.DataFrame.pct_change¶ DataFrame.pct_change (periods = 1, fill_method = 'pad', limit = None, freq = None, ** kwargs) [source] ¶ Percentage change between the current and a prior element. Computes the percentage change from the immediately previous row by default. This is useful in comparing the percentage of change in a time series of elements. Parameters

Calculates the difference of a Dataframe element compared with another element in the Dataframe (default is element in previous row). Parameters periods int, default 1. Periods to shift for calculating difference, accepts negative values. axis {0 or ‘index’, 1 or ‘columns’}, default 0. Take difference over rows (0) or columns (1). Returns Dataframe

##### Comments

- Please provide some data, at least some example of what your current dataframe is, and if possible, what do you expect to achieve and what have you tried so far. That way we can understand the issue and help you achieve a solution, otherwise the question is too broad itself
- can you define
`a month ago`

, is it 30 days ago? - @ Shijith Yes a month is 30 days ago.
- So 1 month before March 1 2020 would be January 31, and 1 month before April 1 would be March 2? Looks like a rather uncommon convention...
- @Celius Stingher I have added added a sample data to the question now
- Thank you @Naman I will try your method. I have edited the question since then. If it helps clarify.