Data Types - R Objects and attributes

In this lecture we're going to start getting into the nitty gritty and the details of R. In particular I'm going to talk about different data types that are used in R and some basic operations on those data types. So first it's important to kind of get the language right correctly. So all the things that you manipulate in R, all the things that we encounter in R, are what might be called objects objects can be all different kinds, can contain all different kinds of data. But everything in R, is an object. So the R has five basic atomic classes of objects. So these are kind of the very low level or, or basic classes of objects and they are character, numeric. So these are like real numbers or decimal numbers. integers, complex numbers, and logicals. So logicals are just true a false type things. And so the most basic object in R is called a vector. And a vector conta-, Can contain multiple copies of, for example, of a single type of object. So you can have a vector of characters or a vector of integers, one thing you cannot do with a standard vector is have mixed types of objects you cannot have a vector of characters and numerics, or numerics and integers, or integers and logicals. It, everything in a vector has to be the same class. Of course, with any great rule, there's always an exception, and this, this one is no exception. So, in this, with vectors, there's one type of vector that can have multiple different types of classes, and that's called a list. So a list is represent as a vector, so there's a se, it's a sequence of objects. But each element of that vector can be a different, can be an object of a different class. So for example, you can have a list. That has a character, that has a numeric, it has a logical. You can have a list that's inside the list and one element of the list can be a data frame so, any element of the list can be anything. And that's an, actually why what makes list so useful. So the list is the one exception to the ot to the. General rule that a vectors can only contain elements of the same class. So you can create an empty vector with the vector function. And the vector function has two basic arguments. The first argument is the class of the object, so the type of object that you want to have in the vector. And the second argument is the length of the vector itself. Perhaps the most important type of object in R of course is the number. So numbers in R are generally treated as what are called numeric objectsum, so pretty much all numbers are treated as double number precision real numbers. So, even if you are looking at a number that's like one or two, R thinks of those numbers as numeric objects there is a way to explicitly say you want an integer and you can specify the L subs, the L suf, the capital L suffix there. So for example, if you just enter the number 1 in R, that gives you a numeric object. But entering 1 with a capital L next to it explicitly gives you an integer. This distinction is not very important right now, but, it will become important later. There's also a special number called inf, which stands for infinity and, and inf is like a real number it can be used in calculations and you will get the expected result. So, for example, if you take one, divide it by zero, you'll get infinity and if you take 1 and divide it by infinity you'll get zero. So, emphasis special number, and you can also have minus infinity, too. There's another special value called NAN or Nan. And this represents an undefined value so you can name it as not a number. So, for example, if you take zero over zero that's not a number It's not defined so you'll get a Nan back Nan can also be thought of as a missing value but we'll talk a little bit more about missing values a little bit later so another thing that, that comes with each object in R is an attribute. So not every, object in R necessarily has attributes, but, but they are, but attributes can be part of an object in R. Some of the most common types of attributes that we'll encounter are namesor dim names, or, or dimension names. A dimension, so a matrix will have dimensions for example it will have a number of rows and a number of columns if you have a multidimensional array you'll have more than two dimensions. The class of the object, so every object will have a class. So for example, numeric objects their class is numeric and integer objects, their class is integer. Every object also has a length. So for a vector it's quite simple the length of the object is just the number of elements in the vector. And then there may be other user-defined attributes or metadatas which, so these are things that you can define separately, for an object using various attribute functions. There is a general function called attributes which allows you to set or modify the attributes for an R object.