Example 7.1: Create a Fibonacci sequence

June 12, 2009

(This article was first published on SAS and R, and kindly contributed to R-bloggers)

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.

A pdf of this example is available here.

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;
proc print data=fibo;

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

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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