A vector of all the negative elements of yĪ vector of all the positive elements of y. ![]() A vector of all the positive elements of y.Therefore, if we want to create a vector called y that contains all of the non-NA values from x, we can use y 0 will give us a vector of logical values the same length as y, with TRUEs corresponding to values of y that are greater than zero and FALSEs corresponding to values of y that are less than or equal to zero. Recall that ! gives us the negation of a logical expression, so !is.na(x) can be read as ‘is not NA’. x # NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA Recall that is.na(x) yields a vector of logical values the same length as x, with TRUEs corresponding to NA values in x and FALSEs corresponding to non-NA values in x. One common scenario when working with real-world data is that we want to extract all elements of a vector that are not NA (i.e., missing data). Let’s start by indexing with logical vectors. Index vectors come in four different flavors – logical vectors, vectors of positive integers, vectors of negative integers, and vectors of character strings – each of which we’ll cover in this lesson. The way you tell R that you want to select some particular elements (i.e., a ‘subset’) from a vector is by placing an ‘index vector’ in square brackets immediately following the name of the vector.įor a simple example, try x to view the first ten elements of x. I’ve created for you a vector called x that contains a random ordering of 20 numbers (from a standard normal distribution) and 20 NAs. By the end of this lesson, you’ll know how to handle each of these scenarios. ![]() ![]() In other words, we want to select some of the numbers in a vector based either on their position in the vector or the value that each number has.įor example, we may only be interested in the first 20 elements of a vector, or only the elements that are not NA, or only those that are positive or correspond to a specific variable of interest. In this lesson, we’ll see how to extract elements from a vector based on some conditions that we specify.
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