Category: Python Answers

Sometimes, we want to change one value based on another value in Python Pandas.

In this article, we’ll look at how to change one value based on another value in Python Pandas.

How to change one value based on another value in Python Pandas?

To change one value based on another value in Python Pandas, we can use the slicing feature.

For instance, we write

import pandas

df = pandas.read_csv("test.csv")
df.loc[df.ID == 103, 'FirstName'] = "Matt"

to read the test.csv into a data frame with read_csv.

Then we use df.loc[df.ID == 103, 'FirstName'] to get the entry with ID 103 and the assign the FirstName value of that entry to 'Matt'.

Conclusion

To change one value based on another value in Python Pandas, we can use the slicing feature.

Sometimes, we want to check if a point is inside a polygon in Python.

In this article, we’ll look at how to check if a point is inside a polygon in Python.

How to check if a point is inside a polygon in Python?

To check if a point is inside a polygon in Python, we can use the shapely library.

To install it, we run

pip install Shapely

Then we use it by writing

from shapely.geometry import Point
from shapely.geometry.polygon import Polygon

point = Point(0.5, 0.5)
polygon = Polygon([(0, 0), (0, 1), (1, 1), (1, 0)])
print(polygon.contains(point))

to create a Point object with the coordinates that we want to check.

And we create a Polygon with a list of points for the polygon.

Next, we call polygon.contains with the point to check if point is inside the polygon with the corner points listed in the list we pass into Polygon.

Conclusion

To check if a point is inside a polygon in Python, we can use the shapely library.

Sometimes, we want to convert Python date string to date object

In this article, we’ll look at how to convert Python date string to date object.

How to convert Python date string to date object?

To convert Python date string to date object, we can use the strptime method.

For instance, we write

import datetime

d = datetime.datetime.strptime('24052010', "%d%m%Y").date()

to call datetime.datetime.strptime with the date string that we want to parse into a datetime object.

And we pass in a string to specify the format of the date string so that strptime can parse it.

Then we call date to return the date object from the parsed datetime object.

Conclusion

To convert Python date string to date object, we can use the strptime method.

Sometimes, we want to compare two dataframes and getting the differences with Python.

In this article, we’ll look at how to compare two dataframes and getting the differences with Python.

How to compare two dataframes and getting the differences with Python?

To compare two dataframes and getting the differences with Python, we can use the concat and drop_duplicates methods.

For instance, we write

df_diff = pd.concat([df1,df2]).drop_duplicates(keep=False)

to concatenate the df1 and df2 data frames together with concat.

And then we call drop_duplicates with keep set to False to return a new data frame that has the entries in df1 and df2 but with the duplicate values dropped.

Conclusion

To compare two dataframes and getting the differences with Python, we can use the concat and drop_duplicates methods.

Sometimes, we want to sum a list of numbers in Python.

In this article, we’ll look at how to sum a list of numbers in Python.

How to sum a list of numbers in Python?

To sum a list of numbers in Python, we can use the sum function.

For instance, we write

s = sum(list_of_nums)

to call sum with the 1ist_of_nums numbers list to sum up all the numbers in the list and return the result.

Conclusion

To sum a list of numbers in Python, we can use the sum function.