Manipulating Numbers

Different operations can be performed on numbers such as rounding (abs, ceiling, floor, round), square rooting (sqrt), retrieving the minimum and maximum (min, max) and performing logarithmic transformation (log, log10, log2). On numeric vectors, one could generate random values (sample), compute the sum or the cumulative sum (cumsum), perform sorting (sort, order), generate series of numbers (seq, seq_len), or summarize values (summary).

> ## Retrieve the absolute value of x
> x <- -2.849
> abs(x)

Exercise 12: Using the functions indicated in bold in the previous paragraph, try to:

• Round number to upper or lower integer with 'ceiling(x)' and 'floor(x)' of x <- 2.849
• Round including one digit. Look at the documentation of 'round' with '?round'
• Compute natural, base 2 and base 10 logarithms of x <- 5. Use log, log2 and log10
• Find the square root of x <- 9

On vectors:

> ## Generate a vector containing 10000 random numbers
> ## The logic here is to extract 10000 values from the vector 1 to 1000000
> randomvec1 <- sample(1:1000000, 10000)
> head(randomvec1)

Exercise 13:

• Extract the minimum and maximum values of randomvec1 with 'min' and 'max'
• Compute the cumulative sum with 'cumsum' of the vector vec1 <- c(1,2,3,4,5) and store the result in the variable 'result_cumsum'
• Create a vector of 10 random values between 1 and 1 000 000. Look at the 'sample'
• Sort the values with the function 'sort'
• Retrieve the indexes for sorting the values with the function 'order'
• Generate values from 1 to 10 by 2 with the function ?seq
• Try generating all values now and do the same thing with the function ?seq_len. Put the result in the variable vector_10.
• Repeat the number 5 ten times with ?rep
• Reverse elements of vector_10 with 'rev'
• Compute the 'sum' of all values from 1 to 10 (use vector_10)
• Compute the 'mean' of all values of vector_10
• Compute a 'summary' of randomvec1

Tip: Try avoiding using ":" to generate series of values. Example: Use seq_len(10) instead of 1:10. The reason is that ':' does not handle correctly the empty sequence case. Try 10:0, it will build a reverse sequence instead of an empty sequence. This is important especially in for loops. Imagine that you want to print all values of a vector, if the vector is empty, seq_len will throw a correct error whereas with ':' it will not.

> test_vec <- vector()
> for(i in 1:length(test_vec)) print(test_vec[i])
> for(i in seq_len(test_vec)) print(test_vec[i])

Note: The brackets can be omitted if a "for" loop contains only one instruction.