[R] Various newbie questions

Philippe de Rochambeau philippe at wwphi.net
Wed Feb 4 12:33:15 CET 2004


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


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


5) How do you determine quartiles in R? Is there a way to determine the 
"semi-inter-quartile deviation" ("écart semi-inter-quartile" in 

Many thanks!

Philippe de Rochambeau

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