Example 7.1: Create a Fibonacci sequence
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The Fibonacci numbers have many mathematical relationships and have been discovered repeatedly in nature. They are constructed as the sum of the previous two values, initialized with the values 1 and 1.Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.
A pdf of this example is available here.
SAS
In SAS, we use the lag function (section 1.4.17, p. 22) to retrieve the last value.
data fibo;
do i = 1 to 10;
fib = sum(fib, lag(fib));
if i eq 1 then fib = 1;
output;
end;
run;
proc print data=fibo;
run;
This generates the following output:
Obs i fib 1 1 1 2 2 1 3 3 2 4 4 3 5 5 5 6 6 8 7 7 13 8 8 21 9 9 34 10 10 55
R
In R we can loop over an array to perform the same job.
len <- 10
fibvals <- numeric(len)
fibvals[1] <- 1
fibvals[2] <- 1
for (i in 3:len) {
fibvals[i] <- fibvals[i-1]+fibvals[i-2]
}
This generates the following output:
> fibvals [1] 1 1 2 3 5 8 13 21 34 55
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