When doing data science sometimes you want to create a sequence based on the length of an existing object. The R programming language has a simple little function for doing this job. It has a single argument, and it is the object you are using. This makes it really simple to use.
Description of the seq along function
The seq along function is the R function that you use to create a sequence vector from another object. It has the format of seq_along(length) where “length” is the object being used to determine the length of the sequence vector. This function produces an integer sequence of the same length as the original object. This saves you one or more extra steps in trying to make such an integer sequence. You will find it particularly handy when you are trying to create a for-loop based on the object you are using as an argument. This is a handy little tool for getting an integer sequence from any object.
How the seq along function works
The seq along function finds the length of the argument object and creates an integer sequence from one to that number. This would even be the case if that object has a missing value in it. The purpose of this operation is simply to create an integer sequence of the same length as another object. Exactly what it determines to be the length depends upon the type of object you are working with. For a data frame, it is the number of columns that the data frame has. However, for a vector, it is just the number of values that it contains. Once you get used to working with it you will not have any problems understanding how it works.
Examples
Here we have three examples of the seq along function in action, each of them shows a different aspect of the function’s operation.
> x = seq_along(1:5)
> x
[1] 1 2 3 4 5
In this example, we simply have a list of numbers from one to five as the argument, and it produces a sequence from one to five.
> x = seq_along(11:20)
> x
[1] 1 2 3 4 5 6 7 8 9 10
In this example, we simply have a list of numbers from eleven to twenty as the argument, and it produces a sequence from one to ten.
> z = c(2, 5, 6, 7, 8, 5, 1)
> x = seq_along(z)
> x
[1] 1 2 3 4 5 6 7
In this example, we simply have a vector of seven numbers as the argument, and it produces a sequence from one to seven.
Application
The seq along function’s main application is in creating an integer list for a loop for an operation iteration on your data object based on its size. If you have a data object and you are creating for-loops for it, then this is the perfect way to get your integer sequence for that loop. Another practical application would be creating a numbered list from the contents of your data object. Any place you can think of for using an integer sequence with your data this operation will come in handy. This is a useful tool, that you may find yourself surprised at how you use it.
The seq along function is a tool, that at first glance, you may not understand how you are going to use it but it has uses that you will find as you learn to work with it. Do not let this little tool slip by you. You are likely to find it a more useful tool than you realize.