Basics and Data Types

Nice intro into R for programmers.

R uses $ in a manner analogous to the way other languages use dot.

R has several one-letter reserved words: c, q, s, t, C, D, F, I, and T.

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Assign a variable

Use <- symbols to assign value to a variable.

> x <- 1
> x
[1] 1

We can assign variable in oposit direction too: 1 -> x

As equivalent, we can use assign function to assign value to a variable.

> assign("x", 1)
> x
[1] 1

Print out value of an object

We can simply type name of a variable and that will print it out by itself. Or we can use print function to print it out.

> x <- 1
> x
[1] 1
> print(x)
[1] 1

Sequence

We can create sequence of number as follows and print it the same way as mentioned above.

> x <- 1:20
> x
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20

Structure of object

Find structure of an object.

> data <- data.frame(1:20)
> str(data)
'data.frame':    20 obs. of  1 variable:
 $ X1.20: int  1 2 3 4 5 6 7 8 9 10 ...

str function is very useful function that display compact structure of an object. It can return about any object, so we can use it also for functions.

> str(lm)
function (formula, data, subset, weights, na.action, method = "qr", model = TRUE, x = FALSE, y = FALSE, qr = TRUE, singular.ok = TRUE,
    contrasts = NULL, offset, ...)

Summary function

In case we want more information about an object, we can use summary function.

> library(datasets)
> str(airquality)
'data.frame':    153 obs. of  6 variables:
 $ Ozone  : int  41 36 12 18 NA 28 23 19 8 NA ...
 $ Solar.R: int  190 118 149 313 NA NA 299 99 19 194 ...
 $ Wind   : num  7.4 8 12.6 11.5 14.3 14.9 8.6 13.8 20.1 8.6 ...
 $ Temp   : int  67 72 74 62 56 66 65 59 61 69 ...
 $ Month  : int  5 5 5 5 5 5 5 5 5 5 ...
 $ Day    : int  1 2 3 4 5 6 7 8 9 10 ...

Arrays

You cannot have array of multiples types. So, you cannot mix integers with strings in one array.

> array(1, 3)
[1] 1 1 1

Now we can play with arrays to find out how they work with types.

> as.array(c(1, 2))
[1] 1 2
> as.array(c(1, "2"))
[1] "1" "2"

Numbers

If you type 1, it gives numeric type 1.But if you type 1L, it give 1 as integer type.

Attributes

An object can have attributes. To access attributes, use attributes(). That allows you to set or modify the attributes.

Vectors

To create empty vector, use this.

vector()

c() function will create a vector. So you can create vector like this:

c(1, 2)
1:2

Or we can create verctor like using vector function.

vector("numeric", length = 10)

What happens if you try to mix types in vecotor? R will try to convert it to the same type. So, a surprise might come out.

That leads to thing that you can convert variables to types using as. Like:

as.numeric(x)

For example, you cannot convert strings to numbers.

List

In list, you can mix types.

list(1, "a")

Recursive lists.

x <- list(list(list(list())))
str(x)
> List of 1
>  $ :List of 1
>   ..$ :List of 1
>   .. ..$ : list()
is.recursive(x)

List is index with double brackets.

Matrices

Special type of vector.

matrix(nrows = 2, ncol = 3)

Or if you want to create matrix with values.

matrix(1:6, nrows = 2, ncol = 3)

Matrix can be created from vector.

v<-1:10
dim(v) <- c(1, 2)

Or you can use cbind or rbind to create matrix.

x <- 1:3
y <- 1:3
cbind(x,y)

Factors

Factor is self-describing categorical data. It can be ordered or not ordered.

Factors can be created with factors() function.

factor(c("a", "b"))

Factores are represented as numbers internally. You can set ordering using level attribute.

factor(c("a", "b"), level=c("a", "b"))

Missing values

You can yous is.na() function to test whether a value is na.

Data Frames

Data frames store tabular data and they can be of different classes. Every raw has names.

> x <- data.frame(a = 1:4, b = c(T, T, F, F))
> x
  a     b
1 1  TRUE
2 2  TRUE
3 3 FALSE
4 4 FALSE

Names

All R objects can have names. It can help to create self-describing data.

> x <- 1:3
> names(x)
NULL
> names(x) <- c("a", "b", "c")
> names(x)
[1] "a" "b" "c"

Lists can have names too.

> x <- list(a=1, b=2)
> x
$a
[1] 1

$b
[1] 2

How to access variable in list.

> x <- list(aa=1)
> x$aa
[1] 1

R will try to determin what variable you want even if you not provide full name.

> x <- list(aa=1)
> x$a
[1] 1

Matrix can have names too (dim names).

> m <- matrix(1:4, nrow=2, ncol=2)
> dimnames(m) <- list(c("a", "b"), c("a", "b"))

> m
  a b
a 1 3
b 2 4