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R – Vector Cumulative Sum (With Examples)

Vectors are used to store one-dimensional data of the same type in R. In this tutorial, we will look at how to get the cumulative sum of a vector in R with the help of some examples.

What is the cumulative sum?

The cumulative sum of a series of values is the sum of values up to that value in our series. For example, for a vector of three values (a1, a2, and a3), the cumulative sum would be a1, a1+a2, and a1+a2+a3. The following image illustrates this with an example.

cumulative sum of a vector of four values

In the above image, we have four values 10, 20, 30, and 40. The cumulative sum for these values is 10, 10+20, 10+20+30, and 10+20+30+40 respectively. Note that the order in which these values appear is important when computing the cumulative sum.

How to calculate the cumulative sum of a vector in R?

You can use the cumsum() function in R to compute the cumulative sum of the values in a vector. Pass the vector as an argument to the function. The following is the syntax –

# cumulative sum of vector x
cumsum(x)

It returns a vector containing the cumulative sum of the values in the passed vector.

Examples

Let’s now look at some examples of using the above syntax.

Cumulative sum of a vector of numbers

Let’s create a vector of some numbers and use the cumsum() function to calculate its cumulative sum. For example, let’s compute the cumulative sum for the vector c(10, 20, 30, 40).

# create a vector
vec <- c(10, 20, 30, 40)
# cumulative sum of vector
print(cumsum(vec))

Output:

[1]  10  30  60 100

We print the resulting cumulative sum. You can see that each value in the cumulative sum vector is the sum of all values till that particular index from the original vector.

Cumulative sum of a vector with NA values

What would happen if you apply the cumsum() function to a vector containing some NA values?

Let’s find out.

For this, we will create a vector with some NA values and then apply the cumsum() function.

# create a vector with NA values
vec <- c(10, 20, NA, 30, NA, 40)
# cumulative sum of vector
print(cumsum(vec))

Output:

[1] 10 30 NA NA NA NA

You can see that we get the cumulative sum till we encounter the first NA in our vector. From this point onwards, the resulting cumulative sum for all the values is NA. This happens because performing any arithmetic operation with NA results in an NA in R.

If you want to compute the cumulative sum irrespective of the NA values, you can first remove the NA values from the vector and then apply the cumsum() function.

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Authors

  • Piyush

    Piyush is a data scientist passionate about using data to understand things better and make informed decisions. In the past, he's worked as a Data Scientist for ZS and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.

  • Gottumukkala Sravan Kumar