How to build a correlation matrix in R?
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# How to build a correlation matrix in R?

This recipe helps you build a correlation matrix in R

0

## Recipe Objective

A correlation matrix is a "square" table which consists of correlation coefficients for a set of variables. They are mainly used to determine relationships between the variables.

There are three main applications of correlation matrix:

1. To explore patterns in a large dataset by summarising it in a form of a table.
2. Used as an input for exploratory data analysis, structural equation models and confirmatory factor analysis.
3. Used as a diagnostic step for checking different analysis. For example, a high correlation coefficients indicates that linear regression is unreliable.

This recipe demonstrates how to build a correlation matrix.

Dataset description: It is the basic data about the customers going to the supermarket mall. The variable that we interested in is Annual.Income which is in 1000s , Spending Score and Age

``` # Data manipulation package library(dplyr) library(tidyverse) ​ # reading a dataset customer_seg = read.csv('Mall_Customers.csv') ​ # selecting the required variables using the select() function customer_seg_var = select(customer_seg, Age, Annual.Income..k..,Spending.Score..1.100.) ​ # summary of the selected variables glimpse(customer_seg_var) ```
```
Observations: 200
Variables: 3
\$ Age                     19, 21, 20, 23, 31, 22, 35, 23, 64, 30, 67, 35…
\$ Annual.Income..k..      15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 19, 19…
\$ Spending.Score..1.100.  39, 81, 6, 77, 40, 76, 6, 94, 3, 72, 14, 99, 1…
```

## STEP 2: Building a correlation matrix

We use cor() function to create a correlation matrix.

Syntax: corr(x, method = )

where:

1. x = dataframe as input
2. method = An arguement which provides us to input a method of calculation in the form of vector. The default is Pearson's
``` customer_seg_var.cor = cor(customer_seg_var) customer_seg_var.cor ```
```	Age	Annual.Income..k..	Spending.Score..1.100.
Age	1.00000000 	-0.012398043	-0.327226846
Annual.Income..k..	-0.01239804 	1.000000000	0.009902848
Spending.Score..1.100.	-0.32722685 	0.009902848	1.000000000
```

Note: The Diagonal elements in the matrix is 1.0 as this is the correlation coefficient of the same variable and the coefficients ranges of -1 to 1

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