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plot(cars)
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swirl()
to course menu.
1: Basic Building Blocks 2: Workspace and Files 3: Sequences of Numbers 4: Vectors 5: Missing Values 6: Subsetting Vectors 7: Matrices and Data Frames 8: Logic 9: Functions 10: lapply and sapply 11: vapply and tapply 12: Looking at Data 13: Simulation 14: Dates and Times 15: Base Graphics
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| | 0%
building blocks of the R programming
language.
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|= | 3% | If at any point you’d like more information | on a particular topic related to R, you can | type help.start() at the prompt, which will | open a menu of resources (either within | RStudio or your default web browser, | depending on your setup). Alternatively, a | simple web search often yields the answer | you’re looking for.
…
|== | 5% | In its simplest form, R can be used as an | interactive calculator. Type 5 + 7 and | press Enter.
5+7 [1] 12
|=== | 8% | R simply prints the result of 12 by | default. However, R is a programming | language and often the reason we use a | programming language as opposed to a | calculator is to automate some process or | avoid unnecessary repetition.
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|==== | 11% | In this case, we may want to use our result | from above in a second calculation. Instead | of retyping 5 + 7 every time we need it, we | can just create a new variable that stores | the result.
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|===== | 13% | The way you assign a value to a variable in | R is by using the assignment operator, | which is just a ‘less than’ symbol followed | by a ‘minus’ sign. It looks like this: <-
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|====== | 16% | Think of the assignment operator as an | arrow. You are assigning the value on the | right side of the arrow to the variable | name on the left side of the arrow.
…load(“~/Alberto_UNED/.RData”)
|======= | 18% | To assign the result of 5 + 7 to a new | variable called x, you type x <- 5 + 7. | This can be read as ‘x gets 5 plus 7’. Give | it a try now.
x<- 5+7
|======== | 21% | You’ll notice that R did not print the | result of 12 this time. When you use the | assignment operator, R assumes that you | don’t want to see the result immediately, | but rather that you intend to use the | result for something else later on.
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|========= | 24% | To view the contents of the variable x, | just type x and press Enter. Try it now.
x [1] 12
|========= | 26% | Now, store the result of x - 3 in a new | variable called y.
y <- x-3
|========== | 29% | What is the value of y? Type y to find out.
y [1] 9
|=========== | 32% | Now, let’s create a small collection of | numbers called a vector. Any object that | contains data is called a data structure | and numeric vectors are the simplest type | of data structure in R. In fact, even a | single number is considered a vector of | length one.
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|============ | 34% | The easiest way to create a vector is with | the c() function, which stands for | ‘concatenate’ or ‘combine’. To create a | vector containing the numbers 1.1, 9, and | 3.14, type c(1.1, 9, 3.14). Try it now and | store the result in a variable called z.
c(1.1, 9, 3.14) [1] 1.10 9.00 3.14
info() for more options.
the vector (1.1, 9, 3.14) to a new variable
called z. Including single spaces after the
commas in the vector is not required, but
helps make your code less cluttered and
more readable.
z <- c(1.1, 9, 3.14)
|============= | 37% | Anytime you have questions about a |
particular function, you can access R’s | built-in help files via the
? command. | For example, if you want more information | on
the c() function, type ?c without the | parentheses that normally follow
a function | name. Give it a try.
?c
|============== | 39% | Type z to view its contents. Notice that | there are no commas separating the values | in the output.
z [1] 1.10 9.00 3.14
there!
|=============== | 42% | You can combine vectors to make a new | vector. Create a new vector that contains | z, 555, then z again in that order. Don’t | assign this vector to a new variable, so | that we can just see the result | immediately.
c(z, 555, z) [1] 1.10 9.00 3.14 555.00 1.10 9.00 [7] 3.14
|================ | 45% | Numeric vectors can be used in arithmetic | expressions. Type the following to see what | happens: z * 2 + 100.
z*2 [1] 2.20 18.00 6.28
again. Or, type info() for more options.
result to a variable. The
* symbol isused for multiplication and shares a key
with the number 8 on many keyboards.
z*2+100 [1] 102.20 118.00 106.28
|================= | 47% | First, R multiplied each of the three | elements in z by 2. Then it added 100 to | each element to get the result you see | above.
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|================== | 50% | Other common arithmetic operators are
+, | -, /, and ^
(where x^2 means ‘x | squared’). To take the square root, use the |
sqrt() function and to take the absolute | value, use the abs()
function.
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|=================== | 53% | Take the square root of z - 1 and assign it | to a new variable called my_sqrt.
my_sqrt <- sqrt(z-1)
|==================== | 55% | Before we view the contents of the my_sqrt | variable, what do you think it contains?
1: a vector of length 0 (i.e. an empty vector) 2: a single number (i.e a vector of length 1) 3: a vector of length 3
Selection: 3
|===================== | 58% | Print the contents of my_sqrt.
my_sqrt [1] 0.3162278 2.8284271 1.4628739
|====================== | 61% | As you may have guessed, R first subtracted | 1 from each element of z, then took the | square root of each element. This leaves | you with a vector of the same length as the | original vector z.
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|======================= | 63% | Now, create a new variable called my_div | that gets the value of z divided by | my_sqrt.
my_div <- z/my_sqrt
|======================== | 66% | Which statement do you think is true?
1: my_div is undefined 2: The first element of my_div is equal to the first element of z divided by the first element of my_sqrt, and so on… 3: my_div is a single number (i.e a vector of length 1)
Selection: 2
|========================= | 68% | Go ahead and print the contents of my_div.
my_div [1] 3.478505 3.181981 2.146460
|========================== | 71% | When given two vectors of the
same length, | R simply performs the specified arithmetic | operation
(+, -, *, etc.) |
element-by-element. If the vectors are of | different lengths, R
‘recycles’ the shorter | vector until it is the same length as the |
longer vector.
…
|=========================== | 74% | When we did z * 2 + 100 in our earlier | example, z was a vector of length 3, but | technically 2 and 100 are each vectors of | length 1.
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|=========================== | 76% | Behind the scenes, R is ‘recycling’ the 2 | to make a vector of 2s and the 100 to make | a vector of 100s. In other words, when you | ask R to compute z * 2 + 100, what it | really computes is this: z * c(2, 2, 2) + | c(100, 100, 100).
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|============================ | 79% | To see another example of how this vector | ‘recycling’ works, try adding c(1, 2, 3, 4) | and c(0, 10). Don’t worry about saving the | result in a new variable.
c(1,2,3,4) + c(0,10) [1] 1 12 3 14
|============================= | 82% | If the length of the shorter vector does | not divide evenly into the length of the | longer vector, R will still apply the | ‘recycling’ method, but will throw a | warning to let you know something fishy | might be going on.
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|============================== | 84% | Try c(1, 2, 3, 4) + c(0, 10, 100) for an | example.
C(1,2,3,4) + c(0, 10, 100) Error in
contrasts<-(*tmp*, how.many, value = contr) : contrasts can be applied only to factors with 2 or more levels c(1,2,3,4) + c(0,10,100) [1] 1 12 103 4 Warning message: In c(1, 2, 3, 4) + c(0, 10, 100) : longer object length is not a multiple of shorter object length
|=============================== | 87% | Before concluding this lesson, I’d like to | show you a couple of time-saving tricks.
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|================================ | 89% | Earlier in the lesson, you computed z * 2 + | 100. Let’s pretend that you made a mistake | and that you meant to add 1000 instead of | 100. You could either re-type the | expression, or…
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|================================= | 92% | In many programming environments, the up | arrow will cycle through previous commands. | Try hitting the up arrow on your keyboard | until you get to this command (z * 2 + | 100), then change 100 to 1000 and hit | Enter. If the up arrow doesn’t work for | you, just type the corrected command.
z*2+1000 [1] 1002.20 1018.00 1006.28
|================================== | 95% | Finally, let’s pretend you’d like to view | the contents of a variable that you created | earlier, but you can’t seem to remember if | you named it my_div or myDiv. You could try | both and see what works, or…
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|=================================== | 97% | You can type the first two letters of the | variable name, then hit the Tab key | (possibly more than once). Most programming | environments will provide a list of | variables that you’ve created that begin | with ‘my’. This is called auto-completion | and can be quite handy when you have many | variables in your workspace. Give it a try. | (If auto-completion doesn’t work for you, | just type my_div and press Enter.)
my_div [1] 3.478505 3.181981 2.146460
En el presente ejercicio 1 de R programing, hemos visto cómo se puede utilizar R como calculadora. Por ejemplo: 5+7 cuyo resultado es 12, lo podemos guardar asignándolo a una variable: x <- 5+7
Se pueden realizar operaciones aritméticas como la variable z multiplicada por 2 y sumarle 100: z*2+100. Esta operación muestra que a cada elemento de la variable z se le multiplica x 2 y se le suma a cada objeto 100.
También hemos aprendido a realizar raíces cuadradas con la función: my_sqrt().