I’ll call that implementation GNU-R to distinguish it from R-language, and from the other implementations I’ll discuss later in the chapter. The most popular implementation is the one from. The implementation is concrete: it reads R code and computes a result. The R-language is abstract: it defines what R code means and how it should work. To understand R’s performance, it helps to think about R as both a language and as an implementation of that language. Let’s get started by learning more about why R is slow. In R’s C interface, you’ll learn a little about R’s C internals. To really understand the performance of built-in base functions, you’ll need to learn a little bit about R’s C API. Rcpp will teach you the absolute minimum you need to know about C++ so you can write fast code using the Rcpp package. In Memory, you’ll learn about how R uses memory, and how garbage collection and copy-on-modify affect performance and memory usage.įor really high-performance code, you can move outside of R and use another programming language. First you figure what’s slow, and then you apply some general techniques to make the slow parts faster. In Profiling, you’ll learn how to systematically make your code faster. The following four chapters will give you the skills to improve the speed of your code when you need to: In this chapter, you’ll learn about some of the trade-offs that R has made, valuing flexibility over performance. The goal of this part of the book is to give you a deeper understanding of R’s performance characteristics. While R is slow compared to other programming languages, for most purposes, it’s fast enough. It was not designed to make life easier for your computer. R was purposely designed to make data analysis and statistics easier for you to do. This is where the brackets brackets.You’re reading the first edition of Advanced R for the latest version see the second edition. Now since a FOR loop structure can contain any number of statements that we may wish for it to execute on each loop through the structure we need to specify in our program which lines or statements of code we intend to be included in the FOR loop structure. If i = 0 and I call i–, i will then equal -1 after I call it.Įach section of the FOR loop declaration statement must be separated by the semicolon: for(section section section). You probably guess that it decreases the value of a variable by 1 every time it is called and is therefore called the decrement operator. If i equals 0 before I call i++, i will be equal to 1 after I call it.Īnother similar symbol is the – symbol. When I call it it simply adds 1 to whatever variable I call it on. The ++ symbol we use in the increment section is called the increment operator - it works just like any counter you can think of in real life. In the condition section ( i < 2 ) we test to see if our counter value ( i ) is equal to our limit/condition value ( 2 ).Īnd in the increment section ( i++ ) we increase the value of our counter value every time we complete a loop of the FOR loop. In the initialization section ( i = 0 ) we initialize our counter value i to the number 0. This statement is broken up into 3 sections: initialization condition increment. Tasks 1 and 3 are handled in the FOR loop declaration: Update my counter value to reflect that we just made it through another loop.Perform the task assigned to the FOR loop - print a message for instance.If the values are not equal then I need to continue performing the task until they are equal. Compare the counter value to the limit value - if my counter value equals my limit value I’m done and the FOR loop has completed it’s task.Now every time my FOR loop goes to do what I’ve assigned it to do I the programmer need to do 3 things: The counter value is the value we use to determine how many times we have performed the task and the limit or condition value is the value we use to determine if we’ve performed the task the amount of times we need to. You could and most of the time would use another variable value like i for the limit/condition value. In the case of this particular problem you are required to use a constant or unchangeable value ( 2 ) as the limit/condition value. The counter value in the case of this problem would be the variable i that was declared at the top:Īnd the limit or condition value would be the number 2: In most instances of FOR loop usage I would need at least 2 separate values: I need a counter value and a limit (condition) value. Each time we perform the task is considered one iteration or loop through the FOR loop. The purpose of the FOR loop is to repeat a task x number of times where x is some dynamic value. Control structures allow the programmer to make decisions in their programs based on changing values like a number supplied by the user for instance. The FOR loop is what is known as a control structure.
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