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genData.Rmd
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genData.Rmd
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## Generating New Data
## Generating New Data
We often want to calculate new variables
Or perhaps make changes to ones we have
We can use <span class="func">mutate</span> or <span class="func">transmute</span> for this
>- <span class='func'>mutate</span> appends to current data
>- <span class='func'>mutate_all</span> will apply a function over multiple columns
>- <span class='func'>mutate_if</span> will apply under some condition
>- <span class='func'>mutate_at</span> will apply to specific columns
>- <span class='func'>transmute</span> will return only the newly created data
First, let's scrape some data:
```{r basketballDataScrape, cache=TRUE, message=FALSE, echo=-1}
library(rvest);
url = "http://www.basketball-reference.com/leagues/NBA_2015_totals.html"
bball = read_html(url) %>%
html_nodes("#totals_stats") %>%
html_table %>%
data.frame %>%
filter(Rk != "Rk")
```
## Generating New Data
The data is currently all character strings
```{r mutateAt0, cache=TRUE}
glimpse(bball[,1:5])
```
## Generating New Data
We'll use <span class='func'>mutate_at</span> to make appropriate columns numeric
- Not Player, Pos, and Tm.
```{r mutateAt, cache=TRUE}
bball = bball %>%
mutate_at(vars(-Player, -Pos, -Tm), funs(as.numeric))
glimpse(bball[,1:7])
```
## Mutate
<span class='func'>mutate</span> takes a vector and returns one of the same dimension
- 'window' function
<br>
We will contrast it with <span class='func'>summarize</span> later
- or <span class='func'>summarise</span> if you prefer
- Takes a vector and returns smaller one (aggregates)
## Generating New Data
A common task- creating composites of existing variables
```{r mutate, cache=TRUE}
bball = bball %>%
mutate(trueShooting = PTS / (2 * (FGA + (.44 * FTA))),
effectiveFG = (FG + (.5 * X3P)) / FGA,
shootingDif = trueShooting - FG.)
summary(select(bball, shootingDif)) # select and others don't have to be piped to use
```
## Generating New Data
Note how we use the new variables
We can use them without quotes
We can use use any variable as soon as it's created
## Generating New Data
Sometimes we want to combine (or split) variables...
<span class='func'>unite</span> creates a string combination of others
- essentially <span class='func'>paste</span>
```{r tidyrUnite, cache=TRUE}
library(tidyr)
bball %>%
unite("posTeam", Pos, Tm) %>%
select(1:5) %>%
head
```
## Generating New Data
<span class='func'>separate</span> does the opposite
Separate player into first and last names based on the space
```{r tidyrSpread, cache=TRUE}
bball %>%
separate(Player, into=c('firstName', 'lastName'), sep=' ') %>%
select(1:5) %>%
head
```
## Your turn
## Your turn
Data: state.x77
- $0.$ Convert to <span class='func'>data.frame</span>
- $1.$ Create a variable that's the <span class='func'>log</span> of <span class="objclass">Population</span> (<span class='func'>mutate</span> )
- $2.$ Create <span class="objclass">curLifeExp</span> as Life Expectancy (<span class="objclass">Life.Exp</span>) + 5 (<span class='func'>mutate</span>)
- $3.$ Summarize the data (<span class='func'>summary</span> )
## Example
```{r yourTurnMutateExample, cache=TRUE}
state.x77 %>%
data.frame %>%
mutate(popLog = log(Population),
curLifeExp = Life.Exp+5) %>%
summary
```