1) What is the difference between a "data frame" (J H Maindonald, Using R, p. 12) and a "vector"?
In Using R, the author asks the reader to enter the following data in a data frame, which I will call "mydata":
year snow.cover 1970 6.5 1971 12.0 1972 14.9 1973 10.0 1974 10.7 1975 7.9 ...
mydata=data.frame(year=c(1970,...),snow.cover=c(6.5,...))
2) How to you retrieve say, snow.cover's second data item? mydata[1][2] does not work, neither does mydata[1,2].
hist(mydata[1,2]) does not work. How would you create a histogram with the above data?
In a French statistics book, the author provides the following data:
Group A Number: 35 Mean:27 Group B Number: 42 Mean:24
and asks: "what is the mean of the group constituted by the reunion of the two groups?"
The answer is of course (27 x 35) + (24 x 42) / 77
3) Is there a way to compute this mean in R (apart from doing the above operation, of course) if you have two sets of data?
4) How do you set class limits in R, for instance
10-20 21-31 etc.
5) How do you determine quartiles in R? Is there a way to determine the "semi-inter-quartile deviation" ("�cart semi-inter-quartile" in French)?
Many thanks!
Philippe de Rochambeau
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