---
title: "Introducing Correlation Funnel - Customer Churn Example"
output: 
  rmarkdown::html_vignette:
    toc: TRUE
vignette: >
  %\VignetteIndexEntry{Introducing Correlation Funnel}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  warning = FALSE,
  message = FALSE,
  dpi = 300
)
```

> Speed Up Exploratory Data Analysis (EDA) with `correlationfunnel`

The goal of `correlationfunnel` is to help data scientist's speed up [Exploratory Data Analysis (EDA)](https://en.wikipedia.org/wiki/Exploratory_data_analysis). EDA can be an incredibly time consuming process. 

## Problem

Traditional approaches to EDA are ___labor intense___ where the data scientist reviews each of the features (predictors) in the data set for relationship to the target (i.e. goal or response). This process of manually building many visualizations and searching for relationships can take hours.

## Solution

<img src="../man/figures/README-corr_funnel.png" width="35%" align="right" style="border-style: solid; border-width: 2px; border-color: #2c3e50; margin-left: 10px; "/>

__Correlation Analysis__ on data that has been _preprocessed_ (more on this shortly) can drastically speed up EDA by identifying key features that relate to the target. The key is getting the features into the "right format". This is where `correlationfunnel` helps.

The `correlationfunnel` package includes a ___streamlined 3-step process for preparing data  and performing visual Correlation Analysis___. The visualization produced uncovers insights by elevating high-correlation features and loweribng low-correlation features. The shape looks like a ___funnel___ (hence the name "Correlation Funnel"), making it very efficient to understand which features are most likely to provide business insights and lend well to a machine learning model. 


## Main Benefits

1. __Speeds Up Exploratory Data Analysis__ - You can drastically increase the speed at which you perform Exploratory Data Analysis (EDA) by using Correlation Analysis to focus on key features (rather than investigating all features).

2. __Improves Feature Selection__ - Using correlation to determine if you have good features prior to spending significant time developing Machine Learning Models.

3. __Gets You To Business Insights Faster__ - Understanding how features are related to a target variable can help you develop the story in the data (aka business insights).

## Correlation Funnel Process

The Correlation Funnel process uses __3 functions__:

1. Transform the data into a binary format with `binarize()` - This step prepares semi-processed data for an optimal format (binary) for correlation analysis

2. Perform correlation analysis using `correlate()` - This step correlates the "binarized" data (binary features) with the target

3. Visualize the feature-target relationships using `plot_correlation_funnel()` - This step produces the visualization from which we can get business insights

## Example - Customer Churn

We'll step through an example of understanding what features are related to Customer Churn. 

Load the necessary libraries.

```{r setup}
library(correlationfunnel)
library(dplyr)
```

Get the `customer_churn_tbl` dataset. The dataset contains a number of features related to a telecommunications company's customer-base and whether or not the customer has churned. The target is "Churn". 

```{r}
data("customer_churn_tbl")

customer_churn_tbl %>% glimpse()
```


### Step 1 - Prepare Data as Binary Features

We use the `binarize()` function to produce a feature set of binary (0/1) variables. Numeric data are binned (using `n_bins`) into categorical data, then all categorical data is one-hot encoded to produce binary features. To prevent low frequency categories (high cardinality categories) from increasing the dimensionality (width of the resulting data frame), we use `thresh_infreq = 0.01` and `name_infreq = "OTHER"` to group excess categories. 

```{r}
customer_churn_binarized_tbl <- customer_churn_tbl %>%
  select(-customerID) %>%
  mutate(TotalCharges = ifelse(is.na(TotalCharges), MonthlyCharges, TotalCharges)) %>%
  binarize(n_bins = 5, thresh_infreq = 0.01, name_infreq = "OTHER", one_hot = TRUE)

customer_churn_binarized_tbl
```

### Step 2 - Correlate to the Target

Next, we use `correlate()` to correlate the binary features to a target (in our case Customer Churn).

```{r}
customer_churn_corr_tbl <- customer_churn_binarized_tbl %>%
  correlate(Churn__Yes)

customer_churn_corr_tbl
```

### Step 3 - Plot the Correlation Funnel

Finally, we visualize the correlation using the `plot_correlation_funnel()` function.

```{r, fig.height=12, fig.width=8, out.height="70%", out.width="70%", fig.align="center"}
customer_churn_corr_tbl %>%
  plot_correlation_funnel()
```

### Business Insights

We can see that the following features are correlated with Churn:

- "Month to Month" Contract Type
- No Online Security
- No Tech Support
- Customer tenure less than 6 months
- Fiber Optic internet service
- Pays with electronic check

We can also see that the following features are correlated with Staying (No Churn):

- "Two Year" Contract Type
- Customer Purchases Online Security
- Customer Purchases Tech Support
- Customer tenure greater than 60 months (5 years)
- DSL internet service
- Pays with automatic credit card

We can then develop a strategy to retain high risk customers:

- Promotions for 2 Year Contract, Online Security, and Tech Support
- Loyalty Bonuses to incentivize tenure
- Incentives for setting up an automatic credit card payment

## Conclusion

The `correlationfunnel` package provides a 3-step workflow that streamlines the EDA process, helps with feature selection, and improves the ease of obtaining Business Insights.

## More Information

To learn about the inner-workings of and key considerations for use of `correlationfunnel`, __please read the Key Considerations and FAQs__. 
