---
title: "Changing Backend File Parser"
author: "Dyfan Jones"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Changing Backend File Parser}
  %\VignetteEngine{knitr::rmarkdown}
  %\usepackage[UTF-8]{inputenc}
---

# Intro
`RAthena` is dependent on `data.table` to read data into `R`. This is down to the amazing speed `data.table` offers when reading files into `R`. However a new package, with equally impressive read speeds, has come onto the scene called [`vroom`](https://github.com/tidyverse/vroom). As `vroom` has been designed to only read data into `R`, similarly to `readr`, `data.table` is still used for all of the heavy lifting. However if a user wishes to use `vroom` as the file parser, `RAthena_options` function has been created to enable this:

```r
library(DBI)
library(RAthena)

con = dbConnect(athena())

RAthena_options(file_parser = c("data.table", "vroom"))
```

By setting the `file_parser` to `"vroom"` then the backend will change to allow `vroom`'s file parser to be used instead of `data.table`. 

# Change back to `data.table`

To go back to using `data.table` as the file parser it is a simple as calling the `RAthena_options` function:

```r
# return to using data.table as file parser
RAthena_options()
```

# Swapping on the fly

This makes it very flexible to swap between each file parser even between each query execution:

```r
library(DBI)
library(RAthena)

con = dbConnect(athena())

# upload data
dbWriteTable(con, "iris", iris)

# use default data.table file parser
df1 = dbGetQuery(con, "select * from iris")

# use vroom as file parser
RAthena_options("vroom")
df2 = dbGetQuery(con, "select * from iris")

# return back to data.table file parser
RAthena_options()
df3 = dbGetQuery(con, "select * from iris")
```

# Why should you consider `vroom`?

If you aren't sure whether to use `vroom` over `data.table`, I draw your attention to `vroom` boasting a whopping 1.40GB/sec throughput.

> *Statistics taken from vroom's github readme* 

package |	version |	time (sec) |	speed-up |	throughput
---|---|---|---|---
vroom |	1.1.0 |	1.14 |	58.44 |	1.40 GB/sec
data.table |	1.12.8 |	11.88 |	5.62 |	134.13 MB/sec
readr |	1.3.1 |	29.02 |	2.30 |	54.92 MB/sec
read.delim |	3.6.2 |	66.74 |	1.00 |	23.88 MB/sec
