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A number of terms crop up throughout this site that may lead to confusion if not addressed properly.

Code and functions

Before diving into terms, we note how we will use fonts in the site. Firstly, any command or object that could be considered code will be shown as code. For example, typing “sum(a + b)” in the console will be shown as sum(a + b). Likewise, functions will always be denoted in this code format, but with the addition of open and closed parentheses. For example, the function “foo” will be denoted as foo().

Variables and objects

In R, a variable refers to the name of a stored value. For example:

my.vector <- c(9, 10, 11)

Here, my.vector holds the vector c(9, 10, 11) and will refer to it when we do operations with my.vector. Sometimes programmers also refer to my.vector as an object since it is a type of object within the syntax of R.

In the EPA API, a variable refers to a desired data filtering characteristic in a URL request. For example, in the URL,

state is considered a variable for the URL since data will be queried according to a particular state.

To avoid confusion, we will always refer to variables referring to the API as an API variable. When dealing with R variables, we will call them an object or specifically call them by their R data type like an R list. For example, through out this tutorial, we will often times reference services or variables. These are both R objects (i.e. a list or dataframe) loaded in with epair, and they are each an R variable containing information about the EPA API.

Parameter codes

In the wider world of mathematics, a parameter can mean a value passed into a function. For example,

foo(a, b)

Here, a and b are considered parameters of the function foo() since they are passed into the function as inputs.

In the EPA API, there are parameter codes. These refer to the particular way an API variable should be used. For instance, taking a look at the URL we showed above,

we see that state = 37. Here, 37 is the parameter code for the state API variable, and this code must be constructed in a particular way to match its API variable. Another example, is with the following URL,

We note that bdate is an API variable referring to the beginning date desired for the data. Its parameter code is 20200101. Likewise, the param API variable has a parameter code of 44201.

In this site, we will refer to values passed into a function as arguments and parameter codes will refer to the encoding value needed in an API variable.