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Basics

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Exercise 2 - Answers

2.1 Create an object named x and assign it the value .x <- sqrt(8)

2.2 Create an object named a and assign it to the value pi. Display the value of a.a <- pia

2.3 Create an object named b and assign it to the value "pi". Display the value of b.b <- "pi"b

2.4 What are the modes of a and b?mode(a)mode(b)

2.5 Without using pi create an object e that has the value .e <- a + 1

2.6 Save e to a file named pi.Rda in your working directory, then remove e from your R workspace, then check it is not in the R workspace.

save(e, file="pi.Rda")rm(e)ls()

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2.7 Load e back to R workspace and check that it is there.load(file="pi.Rda")ls()

2.8 Remove all the objects you created and the file you stored e in. Is your workspace empty?

rm("a","b","e","myObject", "x")file.remove("pi.Rda")ls()

Exercise 2 - Answers cont..

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3.1 Form a vector named j, consisting of the objects b, d and e, with names 'b', 'd' and 'e'. j <- c(b, d, e)names(j) <- c("b", "d", "e")

3.2 What is the mode of j? Check whether j is a vector (Hint: use is.******( ) function).mode(j)is.vector(j)

3.3 Add the elements of vector g named "b" and "d". Do the same for the vector j. Why the error message for one and not the other? Change the mode of the elements in j to numeric and try again.

g["b"] + g["d"]j["b"] + j["d"]as.numeric(j["b"]) + as.numeric(j["d"])

3.4 Replace the "d" element of the vector g with the sum of the elements "b" and "last" of the vector g. What is the value of element "d" of the vector g?

g["d"] <- g["b"] + g["last"]160

3.5 Clean up your workspace, remove all objects.rm(list=ls())ls()

Exercise 3 - Answers

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# Run the following code to create vect1 and vect2:vect1 <- c(rep(1,10), rep(2,10))# Creates a vector named vect1, with length 20, where the first 10 elements

are 1 and next 10# elements are 2.

vect2 <- c(seq(1,30), seq(40,60))# Creates a vector named vect2, which contains the numbers from 1 to 30

and numbers from# 40 to 60.

4.1 Create a vector named vect3, which contains a sample of size 20, without replacement, from the numbers between 1 to 30 and from 40 to 50. Hint, use vect2 and the function sample(). So we can compare answers set a seed of 678. Display vect3.

set.seed(673, kind=NULL);vect3=sample(vect2,20,replace=FALSE)vect3

4.2 Add 1 to the first 10 elements of vect3 and 2 to the next 10 elements. Hint use vect1.

Check your answervect3 <- vect3 + vect1 vect3

4.3 How many elements in vect3 are greater than 25?sum(vect3 > 25) 12

Exercise 4 - Answers

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4.4 How many elements in vect3 are less than 50?sum(vect3 < 50)14

4.5 What is the max of the elements in vect3 which are less than 50?max(vect3[vect3<50])48

4.6 How many elements in vect3 are greater than 25 and less than 50?sum(vect3 > 25 & vect3 < 50)6

4.7 What is the mean of the elements in vect3 are greater than 25 and less than 50?

mean(vect3[vect3 > 25 & vect3 < 50])39.16667

Exercise 4 - Answers cont..

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## Run the following code on the previous slides..h <- c(d, e, f)names(h) <- c("d","e","f")

5.1 What is the mode of i ? What is the mode of h?mode(i)mode(h)

5.2 What is the mode of i[1]? What is the mode of i[[1]]? mode(i[1])mode(i[[1]])

5.3 Print i[[2]] and h[2] and then compare their modes.i[[2]]h[2]mode(i[[2]])mode(h[2])

5.4 Print i[[3]] and h[3] and then compare their modes.i[[3]]h[3]mode(i[[3]])mode(h[2])

Exercise 5 - Answers

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ScenerioYou collected data on one plot today. We need to compile the data in R for

analysis.There were 5 trees: pine, pine, walnut, walnut, alderThe heights were: 100, 75, 120, 90, 50The tree status was: live, live, live, dead, live

6.1 Assign an object named 'tree' to a vector with 5 elements of the tree names.

tree <- c("pine", "pine", "walnut", "walnut", "alder")

6.2 Display the number of elements in the tree vector?length(tree)

6.3 What is the mode of the tree vector?mode(tree)

6.4 Display the number of elements in the tree vector that are "walnut".length(tree[tree == "walnut"])

6.5 Create a vector with 5 elements of tree heights and assign it to an object named 'ht'.

ht <- c(100, 75, 120, 90, 50)

6.6 What is the mode of the ht vector?mode(ht)

6.7 What is the maximum height of all 5 trees?.. what is the average height?

max(ht)mean(ht)

Exercise 6 - Answers

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6.8 Create another vector of 5 elements with tree status and assign to an object named 'status'.

status <- c("live", "live", "live", "dead", "live")

6.9 What is the mode of 'status'?mode(status)

6.10 Change 'status' to a factor with 2 levels, 1:live; 2:dead and assign back to object 'status'.

status <- factor(status, levels=c("live", "dead"))

6.11 Create a data frame object named 'treesdf', with the 3 vectors you just made, 'tree', 'ht', and 'status'.

treesdf <- data.frame(tree, ht, status)

6.12 What are the dimensions of the treesdf?dim(treesdf)

6.13 What are the column names of the data frame?names(treesdf)

6.14 What does the structure of treesdf look like?str(treesdf)

6.15 You missed a tree. It was a dead pine tree with height of 30 meters. Add it to treesdf and assign this new data frame to on object named 'treesdf2'.

treesdf2 <- rbind(treesdf, c("pine", 30, "dead"))

6.16 Save the object, treesdf2 to a file in your workspace named 'treesdf2.Rda'.

save(treesdf2, file="treesdf2.Rda")

Exercise 6 - Answers cont..