date()
## [1] "Thu Sep 27 10:26:33 2012"
Due Date: September 27, 2012
Total Points: 30
1 The following ten observations, taken during the years 1970-1979, are on October snow cover for Eurasia in units of millions of square kilometers. Follow the instructions and answer questions by typing the appropriate R commands.
Year Snow
1970 6.5
1971 12.0
1972 14.9
1973 10.0
1974 10.7
1975 7.9
1976 21.9
1977 12.5
1978 14.5
1979 9.2
a. Create a data frame from these data. (2)
Year = c(1970:1979)
Snow = c(6.5, 12, 14.9, 10, 10.7, 7.9, 21.9, 12.5, 14.5, 9.2)
frame = data.frame(Year, Snow)
frame
## Year Snow
## 1 1970 6.5
## 2 1971 12.0
## 3 1972 14.9
## 4 1973 10.0
## 5 1974 10.7
## 6 1975 7.9
## 7 1976 21.9
## 8 1977 12.5
## 9 1978 14.5
## 10 1979 9.2
b. What are the mean and median snow cover over this decade? (2)
mean(Snow)
## [1] 12.01
median(Snow)
## [1] 11.35
c. What is the standard deviation of the snow cover over this decade? (2)
sd(Snow)
## [1] 4.391
d. How many Octobers had snow cover greater than 10 million km\( ^2 \)? (2)
HeavySnow = which(Snow >= 10) #Heavy snows over 10million km^2
length(HeavySnow)
## [1] 7
2 The data set rivers contains the lengths (miles) of 141 major rivers in North America.
a. What proportion of the rivers are shorter than 500 miles long? (2)
shortriver = which(rivers < 500) #rivers shorter than 500miles
length(shortriver)/length(rivers)
## [1] 0.5816
b. What proportion of the rivers are shorter than the mean length? (2)
avgriver = mean(rivers)
length(which(rivers < avgriver))/length(rivers)
## [1] 0.6667
c. What is the 75th percentile river length? (2)
quantile(rivers, 0.75)
## 75%
## 680
d. What is the interquartile range in river length? (2)
IQR(rivers)
## [1] 370
3 Consider the SSN.txt file on Blackboard. The file contains monthly sunspot numbers for since 1851.
a. Read the data into R to create a data frame. (4)
sunspot = read.table("http://myweb.fsu.edu/jelsner/SSN.txt", header = TRUE)
b. Create a histogram of the September sunspot numbers. (2)
hist(sunspot$Sep)
c. Create a scatter plot placing the June sunspot numbers on the horizontal axis and September sunspot numbers on the vertical axis. (4)
plot(sunspot$Jun, sunspot$Sep, xlab = "June", ylab = "September")
d. Use the grammar of graphics syntax to create a plot showing the September sunspot numbers on the vertical axis and the year on the horizontal axis. (4)
suppressMessages(require(ggplot2))
ggplot(sunspot, aes(Year, Sep)) + geom_point()
