I hope you are doing good.

Please find the answers below:

1. How the data should look like (what cleansing is required) ?

In the dataset, we have columns - spend.category and spend.numeric
The average value of each category of Spend.Category seems to fall within the min and max of each category (e.g. the average spend of the category "$100 - $200" is 146.69889). Hence, Spend.Category is giving us redundant information in a grouped manner. Hence we need to drop the variable "Spend.Category"  of  the dataset in Data cleaning step.

2. How to proceed for sampling ?

The purpose of sampling/ slicing the data into two different sets is as follows: 
  • We will use one part of sliced dataset (trainset) as the dataset which will "train" the model. 
  • The next set (testset) will be used to make our predictions! It is considered a good practice to use two different datasets for training the model and testing the model. 
  • set.seed() is used to enable reproducibility of results when there is randomness involved in any function. In case set.seed is not used, every time a function which involves some randomness (such as sample()) is invoked/ run, it will produce results which will be different for each run/ execution.

Lets say I have data in variable retail_data
index_value = sample(1:nrow(retail_data),size = 0.7*nrow(retail_data)) 

### Retail_Train_Data will contain 70% of the data 
Retail_Train_Data = Retail_Data_Reduced[Index,] 

### Retail_Train_Data will contain the rest 30% of the data 
Retail_Test_Data = Retail_Data_Reduced[-Index,] 

3. How to proceed for Logistic Regression.
I would suggest you to refer to the below link that will help you in working on this project.
Hope this helps you.

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