Cbse class 11, 12, Machine Learning, Data Science and Python

b. Transformations -  This function lets you change the data elements into some other value. Example:- import pandas as pd import numpy as np weather_data = {'Weather': ['Rainy', 'Stormy', 'Sunny', 'Cloudy', 'Rainy', 'Sunny', 'Cloudy', 'Rainy', 'Stormy', 'Cloudy', 'Sunny', 'Sunny'], 'State': ['CG', 'AP', 'HP', 'MP', 'HY','DH' ,'CG' ,'HP','AP' , 'MP','CG','AP'], 'Year': [2014,2015,2014,2015,2014,2015,2016,2017,2016,2014,2015,2017], 'Humidity':[3.4,2.3,3.2,4.7,5.8,8.1,3.2,3.5,7.3,1.1,1.2,2.3]} df = pd.DataFrame(weather_data) gp = df.groupby('Year') print(gp['Humidity']. transform ( lambda x: x*100 )) Output:- 0 340.0 1 230.0 2 320.0 3 470.0 4 580.0 5 810.0 6 320.0 7 350.0 8 730.0 9 1...

2. Applying a function Three types of operation can be performed with groupby function: a. Aggregation b. Transformation c. Filteration a. Aggregation An aggregated function returns a single aggregated value for each group.  Example:- import pandas as pd import numpy as np weather_data = {'Weather': ['Rainy', 'Stormy', 'Sunny', 'Cloudy', 'Rainy', 'Sunny', 'Cloudy', 'Rainy', 'Stormy', 'Cloudy', 'Sunny', 'Sunny'], 'State': ['CG', 'AP', 'HP', 'MP', 'HY','DH' ,'CG' ,'HP','AP' , 'MP','CG','AP'], 'Year': [2014,2015,2014,2015,2014,2015,2016,2017,2016,2014,2015,2017], 'Humidity':[3.4,2.3,3.2,4.7,5.8,8.1,3.2,3.5,7.3,1.1,1.2,2.3]} df = pd.DataFrame(weather_data) grouped = df.groupby('Year') print(grouped['Humidity'].agg(np.sum)) Output:- ...

Aggregation(group by) -  A groupby operation involves some combination of splitting the object, applying a function, and combining the results.  This can be used to group large amounts of data and compute operations on these groups. Groupby function works when you have categorical data as we have in the weather data below. Here 'weather', 'Year'and 'State'are all categorical. Groupby operation involves one of the following operations. Splitting the Object Applying a function    Combining the results gp = df.groupby(['Weather','State']) for name,group in gp: print(name) print(group) Output:- 1. Splitting the object -  import pandas as pd weather_data = {'Weather': ['Rainy', 'Stormy', 'Sunny', 'Cloudy', 'Rainy', 'Sunny', 'Cloudy', 'Rainy', 'Stormy', 'Cloudy', 'Sunny', 'Sunny'], 'State': ['CG...

Transform - This function is used to change the data elements, lets say some data are not how you wannt them to be to process it, usually used during the data preparation step in machine learning. Example1:- import pandas as pd import numpy as np df = pd.DataFrame({'A':range(3),'B':range(1,4)}) print(df.transform(lambda x:x+1)) Output:- A B 0 1 2 1 2 3 2 3 4 Explanation:- range(3) gives a series of number from 0 to 2 range(1,4) gives a series of number from 1 to 3 lambda operator takes each element x and adds 1 to it. Example2:- import pandas as pd import numpy as np s = pd.Series(range(3)) print(s.transform([np.sqrt,np.exp])) Output:- sqrt exp 0 0.000 1.000 1 1.000 2.718 2 1.414 7.389 Explanation:- range(3) gives a series of number from 0 to 2 s.transform function applies two operation(square root and exponential) on each element of series s.

Applymap -  Apply a function to a Dataframe element wise.  This method applies a function that accepts and returns a scalar to every element of a DataFrame. Example:- import pandas as pd import numpy as np df=pd.DataFrame([[1, 2.12], [3.356, 4.567]]) print(df.applymap( lambda x : len(str(x)))) Output:-       0   1 0  3    4 1  5    5 Explanation:- applymap applies particular function to each element of the dataframe. lambda operator is used to create functions without a name. x represent each element of dataframe and len(str(x)) is the operation applied on elements str function is used to convert integer into string len is a function used to calculate the length of the string Quiz:- 1.  import pandas as pd import numpy as np df=pd.DataFrame([[1, 2.12], [3.356, 4.567]])print(df.applymap(lambda x: x**2)) #Post your answer in comment 2.   import pandas as pd import numpy as np ...

Apply -  Apply a function along an axis(rowwise or columnwise) of the DataFrame. Example:- import pandas as pd import numpy as np df = pd.DataFrame({'one':pd.Series([1,2,3,4]),'two':pd.Series([3,5,6,7])}) print(df) print(df.apply(np.mean)) Output:- one two 0 1 3 1 2 5 2 3 6 3 4 7 one 2.50 two 5.25 Explanation:- df is a dataframe object with some float/number data. df.apply(np.mean) applies mean(average) on the index(columnwise/axis=0) by default thats why the output above. df.apply(np.mean,axis=1) applies mean on the columns(Rowwise) and gives output as below one    2.50           two    5.25 Quiz:- 1. import pandas as pd import numpy as np df = pd.DataFrame({'one':pd.Series([1,2,3,4]),'two':pd.Series([3,5,6,7])}) print( df . apply ( np . sum , axis = 0 )) #Post your answer in comment

To apply any built in library functions such as mean, sum etc. to the pandas object(dataframe) or your own functions their are different types of functions Pipe - applies function to the dataframe objects each element. Example:- import pandas as pd import numpy as np def func1(ele1,ele2): return ele1+ele2 df = pd.DataFrame(np.random.randn(5,3),columns=['col1','col2','col3']) print(df) print(df.pipe(func1,10)) Output:- col1 col2 col3 0 0.994857 -0.137329 0.992666 1 0.115403 -1.273267 -0.030973 2 -0.865839 -0.575995 1.629540 3 -0.649246 1.127552 0.750935 4 -0.369847 0.100534 -0.214271 col1 col2 col3 0 10.994857 9.862671 10.992666 1 10.115403 8.726733 9.969027 2 9.134161 9.424005 11.629540 3 9.350754 11.127552 10.750935 4 9.630153 10.100534 9.785729 Explanation:- random.randn(5,3) is a library function found inside numpy module, it creates 5x3 i.e 5 rows and 3 colu...