---
layout: default
title: Data transformation
output: bookdown::html_chapter
---


## Missing values

* Why `NA == NA` is not `TRUE`
* Why default is `na.rm = FALSE`.

## Data types

Overview of different data types and useful summary functions for working with them. Strings and dates covered in more detail in future chapters.  

Need to mention `typeof()` vs. `class()` mostly in context of how date/times and factors are built on top of simpler structures.

### Logical

When used with numeric functions, `TRUE` is converted to 1 and `FALSE` to 0. This makes `sum()` and `mean()` particularly useful: `sum(x)` gives the number of `TRUE`s in `x`, and `mean(x)` gives the proportion.

### Numeric (integer and double)

### Strings (and factors)

### Date/times
