Scripting Loops In R

June 1, 2016
By

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

An R programmer can determine the order of processing of commands, via use of the control statements; `repeat{}`, `while()`, `for()`, `break`, and `next`

Answers to the exercises are available here.

Exercise 1
The `repeat{}` loop processes a block of code until the condition specified by the `break` statement, (that is mandatory within the `repeat{}` loop), is met.

The structure of a `repeat{}` loop is:
```repeat { commands if(condition) { break } }```

For the first exercise, write a `repeat{}` loop that prints all the even numbers from `2``10`, via incrementing the variable, “`i <- 0`“.

Exercise 2
Using the following variables:

`msg <- c("Hello")`
`i <- 1`

Write a `repeat{}` loop that breaks off the incrementation of, “`i`“, after `5` loops, and prints “`msg`” at every increment.

Exercise 3
`while()` loop will repeat a group of commands until the condition ceases to apply. The structure of a `while()` loop is:

```while(condition) { commands }```

With, `i <- 1`, write a `while()` loop that prints the odd numbers from `1` through `7`.

Exercise 4
Using the following variables:

`msg <- c("Hello")`
`i <- 1`

Write a `while()` loop that increments the variable, “`i`“, `6` times, and prints “`msg`” at every iteration.

Exercise 5
The `for()` loop repeats commands until the specified length of the condition is met. The structure of a `for()` loop is:
`for(condition) { commands }`

For example:
```for(i in 1:4) { print("variable"[i]) }```

```for(i in seq("variable")) { print(i) }```

```for(i in seq_along("variable")) { print("variable"[i]) }```

```for(letter in "variable") { print(letter) }```

For this exercise, write a `for()` loop that prints the first four numbers of this sequence: `x <- c(7, 4, 3, 8, 9, 25)`

Exercise 6
For the next exercise, write a `for()` loop that prints all the letters in `y <- c("q", "w", "e", "r", "z", "c").`

Exercise 7
The `break` statement is used within loops to exit from the loop. If the `break` statement is within a nested loop, the inner loop is exited, and the outer loop is resumed.

Using `i <- 1`, write a `while()` loop that prints the variable, “`i`“, (that is incremented from `1``5`), and uses `break` to exit the loop if “`i`” equals `3`.

Exercise 8
Write a nested loop, where the outer `for()` loop increments “`a``3` times, and the inner `for()` loop increments “`b``3` times. The `break` statement exits the inner `for()` loop after `2` incrementations. The nested loop prints the values of variables, “`a`” and “`b`“.

Exercise 9
The `next` statement is used within loops in order to skip the current evaluation, and instead proceed to the next evaluation.

Therefore, write a `while()` loop that prints the variable, “`i`“, that is incremented from `2``5`, and uses the `next` statement, to skip the printing of the number `3`.

Exercise 10
Finally, write a `for()` loop that uses next to print all values except “`3`” in the following variable: `i <- 1:5`

R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.