# Introduction to teal.data

#### NEST CoreDev

# Introduction

The `teal.data` package specifies the data format used in `teal` applications. The `teal_data` class inherits from `qenv` and is meant to be used for reproducibility purposes.

## Quick Start

To create an object of class `teal_data`, use the `teal_data` function. `teal_data` has a number of methods to manage relevant information in private class slots.

    library(teal.data)

    # create teal_data object
    my_data <- teal_data()

    # run code within teal_data to create data objects
    my_data <- within(
      my_data,
      {
        data1 <- data.frame(id = 1:10, x = 11:20)
        data2 <- data.frame(id = 1:10, x = 21:30)
      }
    )

    # get objects stored in teal_data
    my_data[["data1"]]
    my_data[["data1"]]

    # get reproducible code
    get_code(my_data)

    # get or set datanames
    datanames(my_data) <- c("data1", "data2")
    datanames(my_data)

    # print
    print(my_data)

## `teal_data` characteristics

A `teal_data` object keeps the following information:

- `env` - an environment containing data.
- `code` - a string containing code to reproduce `env` (details in reproducibility).
- `datanames` - a character vector listing objects of interest to `teal` modules (details in this `teal` vignette).
- `join_keys` - a `join_keys` object defining relationships between datasets (details in Join Keys).

### Reproducibility

The primary function of `teal_data` is to provide reproducibility of data. We recommend to initialize empty `teal_data`, which marks object as verified, and create datasets by evaluating code in the object, using `within` or `eval_code`. Read more in teal_data Reproducibility.

    my_data <- teal_data()
    my_data <- within(my_data, data <- data.frame(x = 11:20))
    my_data <- within(my_data, data$id <- seq_len(nrow(data)))
    my_data # is verified

    ## ✅︎ verified teal_data object
    ## <environment: 0x7fc10a6a6b40> [L]
    ## Parent: <environment: package:teal.data>
    ## Bindings:
    ## • data: <df[,2]> [L]

### Relational data models

The `teal_data` class supports relational data. Relationships between datasets can be described by joining keys and stored in a `teal_data` object. These relationships can be read or set with the `join_keys` function. See more in join_keys.

    my_data <- teal_data()
    my_data <- within(my_data, {
      data <- data.frame(id = 1:10, x = 11:20)
      child <- data.frame(id = 1:20, data_id = c(1:10, 1:10), y = 21:30)
    })

    join_keys(my_data) <- join_keys(
      join_key("data", "data", key = "id"),
      join_key("child", "child", key = "id"),
      join_key("child", "data", key = c("data_id" = "id"))
    )

    join_keys(my_data)

    ## A join_keys object containing foreign keys between 2 datasets:
    ## child: [id]
    ##   <-- data: [id]
    ## data: [id]
    ##   --> child: [data_id]