# Introduction to teal.data

#### NEST CoreDev

# Introduction

The `teal.data` package specifies the data format used in `teal` applications.

A `teal_data` is meant to be used for reproducibility purposes. The class inherits from `qenv` and we encourage to get familiar with `teal.code` first. `teal_data` has following characteristics:

- It inherits from the environment and methods such as `$`, `get()`, `ls()`, `as.list()` work out of the box.
- `teal_data` is a locked environment, and data modification is only possible through the `teal.code::eval_code()` and `within.qenv()` functions.
- It stores metadata about the code used to create the data (see reproducibility).
- It supports slicing by `[`.
- It is immutable which means that each code evaluation does not modify the original `teal_data` environment directly.
- It maintains information about relationships between datasets (see Join Keys).

## Quick Start

To create an object of class `teal_data`, use the `teal_data` function. `teal_data` has a number of methods to interact with the object.

    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)
        data3 <- data.frame(id = 1:10, x = 31:40)
      }
    )

    # get objects stored in teal_data
    my_data[["data1"]]
    my_data[["data2"]]

    # limit objects stored in teal_data
    my_data[c("data1", "data3")]

    # get reproducible code
    get_code(my_data)

    # get code just for specific object
    get_code(my_data, names = "data2")

    # get datanames
    names(my_data)

    # print
    print(my_data)

### 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

    ## ✅︎ code verified
    ## <environment: 0x11d1d5248> 🔒
    ## Parent: <environment: package:teal.data>
    ## Bindings:
    ## - data: [data.frame]

### 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]

    # join_keys for limited object
    join_keys(my_data["child"])

    ## A join_keys object containing foreign keys between 1 datasets:
    ## child: [id]

### Hidden objects

An object is hidden in `teal_data` if its name starts with a dot (`.`). This can be used to pass auxiliary objects in the `teal_data` instance, without being visible in the `teal` summary and filter panel.

    my_data <- teal_data()
    my_data <- within(my_data, {
      data <- data.frame(id = 1:10, x = 11:20)
      .data2 <- data.frame(id = 1:20, data_id = c(1:10, 1:10), y = 21:30)
    })

    ls(my_data)

    ## [1] "data"

    names(my_data)

    ## [1] "data"