---
title: "R mapping"
author: "John Mount"
date: "`r Sys.Date()`"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{R mapping}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

`rqdatatable` re-maps a number of symbols for `data.table` translation (for `rquery`/`SQL` re-mappings, please see [here](https://winvector.github.io/rquery/articles/R_mapping.html)).  For instance, please take note of the `n()` and `rank()` functions in the following code example.

```{r}
library("rqdatatable")
library("wrapr")

dL <- build_frame(
  "subjectID", "surveyCategory"     , "assessmentTotal"|
    1          , "withdrawal behavior", 5              |
    1          , "positive re-framing", 2              |
    2          , "withdrawal behavior", 3              |
    2          , "positive re-framing", 4              |
    2          , "other"              , 0              )

scale <- 0.237
rquery_pipeline <- local_td(dL) %.>%
  extend_nse(.,
             probability :=
               exp(assessmentTotal * scale)/
               sum(exp(assessmentTotal * scale)),
             count := n(),
             rank := rank(),
             orderby = c("assessmentTotal", "surveyCategory"),
             reverse = c("assessmentTotal"),
             partitionby = 'subjectID')  %.>%
  orderby(., c("subjectID", "probability"))
res <- ex_data_table(rquery_pipeline, tables = list(dL = dL))
knitr::kable(res)
```

The common re-mappings are can be found in the package-private variable `rqdatatable:::data_table_extend_fns`.

```{r}
str(rqdatatable:::data_table_extend_fns)
```

The column `rqdatatable_temp_one_col` is introduced (and removed) from intermediate data frames as needed.

These mappings help allow the same operator pipeline to be used in `R` and in a database. For the database mappings please see [here](https://winvector.github.io/rquery/articles/R_mapping.html).