Visualising numerical data

# Visualising numerical data
## <br><br> Introduction to Data Science with R and Tidyverse
### based on datasciencebox.org

---

layout: true
  
<div class="my-footer">
<span>
Introduction to Data Science with R and Tidyverse | Lukas Jürgensmeier, Matteo Fina, Jan Bischoff | based on
<a href="https://datasciencebox.org" target="_blank">datasciencebox.org</a>
</span>
</div>

---

# Terminology

---

.pull-left[
## Number of variables
Data analysis can be
- **Univariate** (one variable)
- **Bivariate** (two variables)
- **Multivariate** (several variables and their conditional relationship)
]
.pull-right[
## Types of variables
Two main types of variables:
- **Numerical variables** can be classified as **continuous** or **discrete** based on whether or not the variable can take on an infinite number of values or only non-negative whole numbers, respectively.
- If the variable is **categorical**, we can determine if it is **ordinal** based on whether or not the levels have a natural ordering.
]

---

# Data

---

## Data: Lending Club

- Thousands of loans made through the Lending Club, which is a platform that allows individuals to lend to other individuals

- Not all loans are created equal -- ease of getting a loan depends on (apparent) ability to pay back the loan

- Data includes loans *made*, these are not loan applications
]
.pull-right-narrow[
<img src="img/lending-club.png" width="100%" style="display: block; margin: auto;" />
]

---

## Take a peek at data

```r
library(openintro)
glimpse(loans_full_schema)
```

```
## Rows: 10,000
## Columns: 55
## $ emp_title                        <chr> "global config enginee~
## $ emp_length                       <dbl> 3, 10, 3, 1, 10, NA, 1~
## $ state                            <fct> NJ, HI, WI, PA, CA, KY~
## $ homeownership                    <fct> MORTGAGE, RENT, RENT, ~
## $ annual_income                    <dbl> 90000, 40000, 40000, 3~
## $ verified_income                  <fct> Verified, Not Verified~
## $ debt_to_income                   <dbl> 18.01, 5.04, 21.15, 10~
## $ annual_income_joint              <dbl> NA, NA, NA, NA, 57000,~
## $ verification_income_joint        <fct> , , , , Verified, , No~
## $ debt_to_income_joint             <dbl> NA, NA, NA, NA, 37.66,~
## $ delinq_2y                        <int> 0, 0, 0, 0, 0, 1, 0, 1~
## $ months_since_last_delinq         <int> 38, NA, 28, NA, NA, 3,~
## $ earliest_credit_line             <dbl> 2001, 1996, 2006, 2007~
## $ inquiries_last_12m               <int> 6, 1, 4, 0, 7, 6, 1, 1~
## $ total_credit_lines               <int> 28, 30, 31, 4, 22, 32,~
## $ open_credit_lines                <int> 10, 14, 10, 4, 16, 12,~
...
```

---

## Selected variables

```r
loans <- loans_full_schema %>%
  select(loan_amount, interest_rate, term, grade, 
         state, annual_income, homeownership, debt_to_income)
glimpse(loans)
```

```
## Rows: 10,000
## Columns: 8
## $ loan_amount    <int> 28000, 5000, 2000, 21600, 23000, 5000, 2~
## $ interest_rate  <dbl> 14.07, 12.61, 17.09, 6.72, 14.07, 6.72, ~
## $ term           <dbl> 60, 36, 36, 36, 36, 36, 60, 60, 36, 36, ~
## $ grade          <ord> C, C, D, A, C, A, C, B, C, A, C, B, C, B~
## $ state          <fct> NJ, HI, WI, PA, CA, KY, MI, AZ, NV, IL, ~
## $ annual_income  <dbl> 90000, 40000, 40000, 30000, 35000, 34000~
## $ homeownership  <fct> MORTGAGE, RENT, RENT, RENT, RENT, OWN, M~
## $ debt_to_income <dbl> 18.01, 5.04, 21.15, 10.16, 57.96, 6.46, ~
```

---

## Selected variables

<br>

.midi[
variable        | description
----------------|-------------
`loan_amount`   |	Amount of the loan received, in US dollars
`interest_rate` |	Interest rate on the loan, in an annual percentage
`term`	        | The length of the loan, which is always set as a whole number of months
`grade`	        | Loan grade, which takes a values A through G and represents the quality of the loan and its likelihood of being repaid
`state`         |	US state where the borrower resides
`annual_income` |	Borrower’s annual income, including any second income, in US dollars
`homeownership`	| Indicates whether the person owns, owns but has a mortgage, or rents
`debt_to_income` | Debt-to-income ratio
]

---

## Variable types

<br>

variable        | type
----------------|-------------
`loan_amount`   |	numerical, continuous
`interest_rate` |	numerical, continuous
`term`	        | numerical, discrete
`grade`	        | categorical, ordinal
`state`         |	categorical, not ordinal
`annual_income` |	numerical, continuous
`homeownership`	| categorical, not ordinal
`debt_to_income` | numerical, continuous

---

# Visualizing numerical data

---

## Describing shapes of numerical distributions

- shape:
    - skewness: right-skewed, left-skewed, symmetric (skew is to the side of the longer tail)
    - modality: unimodal, bimodal, multimodal, uniform
- center: mean (`mean`), median (`median`), mode (not always useful)
- spread: range (`range`), standard deviation (`sd`), inter-quartile range (`IQR`)
- unusual observations

---

# Histogram

---

## Histogram

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_histogram()
```

```
## `stat_bin()` using `bins = 30`. Pick better value with
## `binwidth`.
```

---

## Histograms and binwidth

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_histogram(binwidth = 1000)
```

<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-6-1.png" width="50%" style="display: block; margin: auto;" />
]
.panel[.panel-name[binwidth = 5000]

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_histogram(binwidth = 5000)
```

<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-7-1.png" width="50%" style="display: block; margin: auto;" />
]
.panel[.panel-name[binwidth = 20000]

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_histogram(binwidth = 20000)
```

<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-8-1.png" width="50%" style="display: block; margin: auto;" />
]
]

---

## Customizing histograms

.panelset[
.panel[.panel-name[Plot]
<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-9-1.png" width="60%" style="display: block; margin: auto;" />
]
.panel[.panel-name[Code]

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_histogram(binwidth = 5000) +
* labs(
*   x = "Loan amount ($)",
*   y = "Frequency",
*   title = "Amounts of Lending Club loans"
* )
```
]
]

---

## Fill with a categorical variable

.panelset[
.panel[.panel-name[Plot]
<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-10-1.png" width="60%" style="display: block; margin: auto;" />
]
.panel[.panel-name[Code]

```r
ggplot(loans, aes(x = loan_amount, 
*                 fill = homeownership)) +
  geom_histogram(binwidth = 5000,
*                alpha = 0.5) +
  labs(
    x = "Loan amount ($)",
    y = "Frequency",
    title = "Amounts of Lending Club loans"
  )
```
]
]

---

## Facet with a categorical variable

.panelset[
.panel[.panel-name[Plot]
<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-11-1.png" width="60%" style="display: block; margin: auto;" />
]
.panel[.panel-name[Code]

```r
ggplot(loans, aes(x = loan_amount, fill = homeownership)) + 
  geom_histogram(binwidth = 5000) +
  labs(
    x = "Loan amount ($)",
    y = "Frequency",
    title = "Amounts of Lending Club loans"
  ) +
* facet_wrap(~ homeownership, nrow = 3)
```
]
]

---

# Density plot

---

## Density plot

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_density()
```

---

## Density plots and adjusting bandwidth

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_density(adjust = 0.5)
```

<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-13-1.png" width="50%" style="display: block; margin: auto;" />
]
.panel[.panel-name[adjust = 1]

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_density(adjust = 1) # default bandwidth
```

<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-14-1.png" width="50%" style="display: block; margin: auto;" />
]
.panel[.panel-name[adjust = 2]

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_density(adjust = 2)
```

<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-15-1.png" width="50%" style="display: block; margin: auto;" />
]
]

---

## Customizing density plots

.panelset[
.panel[.panel-name[Plot]
<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-16-1.png" width="60%" style="display: block; margin: auto;" />
]
.panel[.panel-name[Code]

```r
ggplot(loans, aes(x = loan_amount)) +
  geom_density(adjust = 2) +
* labs(
*   x = "Loan amount ($)",
*   y = "Density",
*   title = "Amounts of Lending Club loans"
* )
```
]
]

---

## Adding a categorical variable

.panelset[
.panel[.panel-name[Plot]
<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-17-1.png" width="60%" style="display: block; margin: auto;" />
]
.panel[.panel-name[Code]

```r
ggplot(loans, aes(x = loan_amount, 
*                 fill = homeownership)) +
  geom_density(adjust = 2, 
*              alpha = 0.5) +
  labs(
    x = "Loan amount ($)",
    y = "Density",
    title = "Amounts of Lending Club loans", 
*   fill = "Homeownership"
  )
```
]
]

---

# Box plot

---

## Box plot

```r
ggplot(loans, aes(x = interest_rate)) +
  geom_boxplot()
```

---

## Box plot and outliers

```r
ggplot(loans, aes(x = annual_income)) +
  geom_boxplot()
```

---

## Customizing box plots

.panelset[
.panel[.panel-name[Plot]
<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-20-1.png" width="60%" style="display: block; margin: auto;" />
]
.panel[.panel-name[Code]

```r
ggplot(loans, aes(x = interest_rate)) +
  geom_boxplot() +
  labs(
    x = "Interest rate (%)",
    y = NULL,
    title = "Interest rates of Lending Club loans"
  ) +
* theme(
*   axis.ticks.y = element_blank(),
*   axis.text.y = element_blank()
* )
```
]
]

---

## Adding a categorical variable

.panelset[
.panel[.panel-name[Plot]
<img src="u2-d03-viz-num_files/figure-html/unnamed-chunk-21-1.png" width="60%" style="display: block; margin: auto;" />
]
.panel[.panel-name[Code]

```r
ggplot(loans, aes(x = interest_rate,
*                 y = grade)) +
  geom_boxplot() +
  labs(
    x = "Interest rate (%)",
    y = "Grade",
    title = "Interest rates of Lending Club loans",
*   subtitle = "by grade of loan"
  )
```
]
]

---

# Relationships numerical variables

---

## Scatterplot

```r
ggplot(loans, aes(x = debt_to_income, y = interest_rate)) +
  geom_point()
```