What does the diff() function in R do? [closed]

Question

I do not understand what the function diff() in R does. See this example:

 temp = c(10,1,1,1,1,1,1,2,1,1,1,1,1,1,1,3,10)  diff(temp) 

The above code produces the following output:

 [1] -9  0  0  0  0  0  1 -1  0  0  0  0  0  0  2  7 

What is the definition of this function?

Answer 1

The function calculates the differences between all consecutive values of a vector. For your example vector, the differences are:

 1 - 10 = -9  1 -  1 =  0  1 -  1 =  0 . . .  3 -  1 =  2 10 -  3 =  7 

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The argument differences allows you to specify the order of the differences.

E.g., the command

diff(temp, differences = 2)  [1]  9  0  0  0  0  1 -2  1  0  0  0  0  0  2  5 

produces the same result as

diff(diff(temp)) [1]  9  0  0  0  0  1 -2  1  0  0  0  0  0  2  5 

Hence, it returns the differences of differences.

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The argument lag allows you to specify the lag.

For example, if lag = 2, the differences between the third and the first value, between the fourth and the second value, between the fifth and the third value etc. are calculated.

diff(temp, lag = 2) [1] -9  0  0  0  0  1  0 -1  0  0  0  0  0  2  9 

Answer 2

It computes the difference between pairs of consecutive elements.

Let's say temp are observations of some variable, for example temperature readings taken on the hour. Then diff(temp) will tell you how much the temperature has changed during every hour.

The opposite of diff() is cumsum() (cumulative sum):

> temp  [1] 10  1  1  1  1  1  1  2  1  1  1  1  1  1  1  3 10 > cumsum(c(10, diff(temp)))  [1] 10  1  1  1  1  1  1  2  1  1  1  1  1  1  1  3 10