{"id":127407,"date":"2022-08-20T16:13:15","date_gmt":"2022-08-20T16:13:15","guid":{"rendered":"https:\/\/blog.finxter.com\/?p=595293"},"modified":"2022-08-20T16:13:15","modified_gmt":"2022-08-20T16:13:15","slug":"how-to-apply-a-function-to-each-cell-in-a-pandas-dataframe","status":"publish","type":"post","link":"https:\/\/sickgaming.net\/blog\/2022\/08\/20\/how-to-apply-a-function-to-each-cell-in-a-pandas-dataframe\/","title":{"rendered":"How to Apply a Function to Each Cell in a Pandas DataFrame?"},"content":{"rendered":"\n
\n
\n
\n
\n
<\/div>\n<\/p><\/div>\n
\n
<\/div>\n<\/p><\/div>\n
\n
<\/div>\n<\/p><\/div>\n
\n
<\/div>\n<\/p><\/div>\n
\n
<\/div>\n<\/p><\/div>\n<\/p><\/div>\n
\n
\n
<\/div>\n<\/p><\/div>\n
\n
<\/div>\n<\/p><\/div>\n
\n
<\/div>\n<\/p><\/div>\n
\n
<\/div>\n<\/p><\/div>\n
\n
<\/div>\n<\/p><\/div>\n<\/p><\/div>\n<\/div>\n
5\/5 – (1 vote) <\/div>\n<\/div>\n

Problem Formulation<\/h2>\n

Given the following DataFrame df<\/code>:<\/p>\n

import pandas as pd df = pd.DataFrame([{'A':1, 'B':2, 'C':2, 'D':4}, {'A':4, 'B':8, 'C':3, 'D':1}, {'A':2, 'B':7, 'C':1, 'D':2}, {'A':3, 'B':5, 'C':1, 'D':2}]) print(df) ''' A B C D\n0 1 2 2 4\n1 4 8 3 1\n2 2 7 1 2\n3 3 5 1 2 '''<\/pre>\n
\"\ud83d\udcac\" Challenge<\/strong>: How to apply a function f<\/code> to each cell in the DataFrame? <\/p>\n
For example, you may want to apply a function that replaces all odd values with the value 'odd'<\/code>.<\/p>\n
import pandas as pd df = pd.DataFrame([{'A':1, 'B':2, 'C':2, 'D':4}, {'A':4, 'B':8, 'C':3, 'D':1}, {'A':2, 'B':7, 'C':1, 'D':2}, {'A':3, 'B':5, 'C':1, 'D':2}]) def f(cell): if cell%2 == 1: return 'odd' return cell # ... <Apply Function f to each cell> ... print(df) ''' A B C D\n0 odd 2 2 4\n1 4 8 odd odd\n2 2 odd odd 2\n3 odd odd odd 2 '''<\/pre>\n
Solution: DataFrame applymap()<\/h2>\n
The Pandas DataFrame df.applymap()<\/code> method returns a new DataFrame where the function f<\/code> is applied to each cell of the original DataFrame df<\/code>. You can pass any function object as a single argument into the df.applymap()<\/code> function, either defined as a lambda expression or a normal function.<\/p>\n
Example 1: Replace Odd Values in DataFrame<\/h2>\n
Here’s an example where each cell of the DataFrame is checked against whether it is an odd value. If so, it is replaced with the string 'odd'<\/code>:<\/p>\n
def f(cell): if cell%2 == 1: return 'odd' return cell df_new = df.applymap(f) print(df_new) ''' A B C D\n0 odd 2 2 4\n1 4 8 odd odd\n2 2 odd odd 2\n3 odd odd odd 2 '''\n<\/pre>\n
Example 2: Create Two DataFrames with Even and Odd Values Replaced<\/h2>\n
A slightly advanced example uses two lambda functions<\/a> to create two new DataFrames where one has all odd and the other has all even values replaced:<\/p>\n
import pandas as pd df = pd.DataFrame([{'A':1, 'B':2, 'C':2, 'D':4}, {'A':4, 'B':8, 'C':3, 'D':1}, {'A':2, 'B':7, 'C':1, 'D':2}, {'A':3, 'B':5, 'C':1, 'D':2}]) df_even = df.applymap(lambda x: 'odd' if x%2 else x)\ndf_odd = df.applymap(lambda x: x if x%2 else 'even') print(df_even) ''' A B C D\n0 odd 2 2 4\n1 4 8 odd odd\n2 2 odd odd 2\n3 odd odd odd 2 ''' print(df_odd) ''' A B C D\n0 1 even even even\n1 even even 3 1\n2 even 7 1 even\n3 3 5 1 even '''<\/pre>\n
We used the concept of a ternary operator<\/em><\/strong> to concisely define the replacement function using the keyword lambda<\/a><\/code> to create a function object “on the fly”. <\/p>\n
\"\ud83c\udf0d\" Recommended Tutorial<\/strong>: Understanding the Ternary Operator in Python<\/a><\/p>\n
This tutorial idea was proposed by Finxter student<\/a> Kyriakos<\/strong>. \"\u2764\"<\/p>\n","protected":false},"excerpt":{"rendered":"
5\/5 – (1 vote) Problem Formulation Given the following DataFrame df: import pandas as pd df = pd.DataFrame([{‘A’:1, ‘B’:2, ‘C’:2, ‘D’:4}, {‘A’:4, ‘B’:8, ‘C’:3, ‘D’:1}, {‘A’:2, ‘B’:7, ‘C’:1, ‘D’:2}, {‘A’:3, ‘B’:5, ‘C’:1, ‘D’:2}]) print(df) ”’ A B C D 0 1 2 2 4 1 4 8 3 1 2 2 7 1 2 3 […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[857],"tags":[73,468,528],"class_list":["post-127407","post","type-post","status-publish","format-standard","hentry","category-python-tut","tag-programming","tag-python","tag-tutorial"],"_links":{"self":[{"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/posts\/127407","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/comments?post=127407"}],"version-history":[{"count":0,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/posts\/127407\/revisions"}],"wp:attachment":[{"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/media?parent=127407"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/categories?post=127407"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/tags?post=127407"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}