date()
## [1] "Thu Sep 27 11:59:58 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 = 1970:1979
snow = c(6.5, 12, 14.9, 10, 10.7, 7.9, 21.9, 12.5, 14.5, 9.2)
oct = data.frame(year = year, snow = snow)
b. What are the mean and median snow cover over this decade? (2)
snow_mean = mean(oct$snow)
snow_median = median(oct$snow)
c. What is the standard deviation of the snow cover over this decade? (2)
sd(oct$snow)
## [1] 4.391
d. How many Octobers had snow cover greater than 10 million km\( ^2 \)? (2)
sum(oct$snow > 10)
## [1] 6
2 The data set rivers contains the lengths (miles) of 141 major rivers in North America.
a. What proportion of the rivers are shorter than 500 miles long? (2)
sum(rivers < 500)/length(rivers)
## [1] 0.5816
b. What proportion of the rivers are shorter than the mean length? (2)
avg = mean(rivers)
sum(rivers < avg)/length(rivers)
## [1] 0.6667
c. What is the 75th percentile river length? (2)
quantile(rivers, probs = c(0.75))
## 75%
## 680
d. What is the interquartile range in river length? (2)
IQR(rivers)
## [1] 370
3 Consider the SSN.txt file on Blackboard. The file contains monthly sunspot numbers for since 1851.
a. Read the data into R to create a data frame. (4)
loc = "http://myweb.fsu.edu/jelsner/SSN.txt"
SSN = read.table(loc, header = TRUE)
b. Create a histogram of the September sunspot numbers. (2)
hist(SSN$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(SSN$Jun, SSN$Sep)
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)
plot(SSN$Year, SSN$Sep)
