Manipulating Vectors

Several functions enable to compare and manipulate vectors:

> vec1 <- c(1,2,3,4)
> vec2 <- c(2,3,4,5)
> vec3 <- c(1,2,5,6)
> vec4 <- c(2,4,5,5,4,1)
> vec5 <- c("A", "A", "C", "T", "G", "T")
>
> ## Get the number of elements of a vector (or a list)
> length(vec2)

Exercise 15:

• Verify if all the values of vec2 are higher than the values of vec1 with all.
• Verify if all the values of vec3 are equal to the values of vec1 with all.equal.
• Verify if any of the value of vec3 is higher than the values of vec1 with any.
• Find the duplicated values of vec4 with duplicated.
• Find if any of the values of vec4 or vec5 are duplicated with anyDuplicated.
• Remove duplicated values from vec4 and vec5 with unique.
• Make the elements of vec5 unique with make.unique.
• Create a list 'list_vec' with the vectors vec1 to vec4
• Use a for loop to print each vector
• Modify the for loop to print from vec2 to vec4 (omitting vec1)
• Do a 2 by 2 comparison of the equality of the vectors using a double for loop

TIP: If you want to compare two values, use also the isTRUE(all.equal()) form. The reason is that the way R stores floating values in memory can be tricky. Test the code below and identify what is wrong:

> x = seq(0,1,by=0.2)
> y = c(0.0, 0.2, 0.4, 0.6, 0.8, 1.0)
>
> x
> y
>
> x == y
> all(x == y)
> all.equal(x,y)
>
> x[4] == y[4]
> all.equal(x[4],y[4])

R represents missing values by NA (Not Available). You will very often find NA values when reading public data or your own table. The reasons for having missing values can be multiple: Lack of experimental data, error in reading functions, etc. A lot of functions in R have a parameter to handle missing values, usually it is denoted by 'na.rm' (rm = remove). Two important functions for handling NA values are is.na and anyNA:

> x <- NA
> y <- 10
> z <- 32
> vec6 <- c(x,y,z)
> is.na(x)
> is.na(y)
> is.na(z)
> is.na(vec6)
> anyNA(vec6)

Exercise 16:

• Remove duplicated values from vec5 and display it in reverted order
• Add vec6 to list_vec
• Using a for loop, display the vector of list_vec having missing values

Very often it is necessary to find the elements of a vector satisfying a particular condition. The function which is very useful to achieve such goal is which:

> ## Find the elements of vec4 that are higher than 3
> which(vec4 > 3)

Exercise 17:

• Find the elements of vec4 that are higher than 3 and lower than 5
• Find the index of the minimum and maximum of vec4 with which.min and which.max.