mapply and Map in R

[This article was first published on R – Open Source Automation, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

Map and mapply in r

An older post on this blog talked about several alternative base apply functions. This post will talk about how to apply a function across multiple vectors or lists with Map and mapply in R. These functions are generalizations of sapply and lapply, which allow you to more easily loop over multiple vectors or lists simultaneously.


Suppose we have two lists of vectors and we want to divide the nth vector in one list by the nth vector in the second list. Map makes this straightforward to accomplish, while keeping the code clean to read. Map returns a list by default, similar to lapply.

Below, we create two sample lists of vectors.

values1 <- list(a = c(1, 2, 3), b = c(4, 5, 6), c = c(7, 8, 9))

values2 <- list(a = c(10, 11, 12), b = c(13, 14, 15), c = c(16, 17, 18)) 

Now, let’s do the operation we described above using Map. Here, we’ll input the function as the first parameter. In this case, the function takes two numeric values as input and divides the first value by the second. The remaining inputs to Map are the names of the lists we are looping over.

Map(function(num1, num2) num1 / num2, values1, values2)

num1 refers to each individual element in the iteration over values1, while num2 refers to each individual element in the iteration over values2. Each element in each list is a vector.

Map function in r

Below is another example. Here, we loop over our two lists of vectors, and get the pairwise union of the vectors across the lists.

Map(function(num1, num2) union(num1, num2), values1, values2)


mapply, similar to sapply, tries to return a vector result when possible. Like Map, one difference between mapply and sapply or lapply is that the function to be applied is input as the first parameter.

Let’s suppose we again have our two lists of vectors, but this time we want to get the maximum value across two pairwise vectors for each pair of vectors in the lists.

mapply(function(num1, num2) max(c(num1, num2)), values1, values2)

mapply example in r

Here, mapply loops over each of the lists simultaneously. For the nth vector in each list, mapply combines the two vectors and finds the maximum value.

Map is actually a wrapper around mapply, with the parameter SIMPLIFY set to FALSE. Setting this parameter to TRUE (which is default) means (as mentioned above) mapply will try to simplify the result to a vector if possible. Each of these functions can also be useful in iterating over lists of data frames.

That’s it for this post. Please click here to follow my blog on Twitter!

The post mapply and Map in R appeared first on Open Source Automation.

To leave a comment for the author, please follow the link and comment on their blog: R – Open Source Automation. offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)