---
title: "Examples - Using pivot_longer() and pivot_wider()"
output:
  word_document: default
  pdf_document: default
  html_notebook: default
---

# Example of *tibble()* and *tribble()* functions to create a data_frame.

```{r message=FALSE}
library(tidyverse)

BP_narrow <- tibble(
  x = c("a", "b"),
  y = c(1,2),
  z = c(3.6, 8.5)
)

BP_narrow <- tribble(
  ~x, ~y,  ~z,
  "a", 2,  3.6,
  "b", 1,  8.5
)
```

```{r}
BP_narrow <- tribble(
  ~subject, ~when, ~spb,
  "BHO", "before", 160,
  "GWB", "before", 120,
  "WJC", "before", 105,
  "BHO", "after", 115,
  "GWB", "after", 135,
  "WJC", "after", 145
)
```

# Examples of *pivot_longer()* and *pivot_wider()*

```{r}
BP_wide <- BP_narrow %>% pivot_wider(names_from = "when", values_from = "spb")
BP_wide
```


```{r}
BP_narrow_new <- BP_wide %>% pivot_longer(c("before", "after"), names_to = "when", values_to = "spb" )

BP_narrow_new 
```

Or we can remove the *subject* column and use the remaining two columns *before* and *after*. 

```{r}
BP_narrow_new <- BP_wide %>% pivot_longer(-subject, names_to = "when", values_to = "spb" )

BP_narrow_new 
```

# Example *spread()*

Try the code in Section 5.2.4 on pages 101-103.  Try to use the new *pivot_wider()* function.

```{r}
library(babynames)

babynames
```

# Example *for*

Try the code on pages 104-105

# Example *apply()*

Try the code on pages 106-107

Next week we will take a look at the *map* functions from the *purrr* R package, which are modern alternatives to *for* loops and the *apply()* functions.