Consider the following graph of air quality measurements taken hourly in Beijing. This type of scheme is really useful for putting different colors in graphs for different conditions. The logic by which this will assign grades is depicted in the figure below. We can use a "nested" ifelse command as follows: "A" if 90≤final_score Nested ifelse Statements Suppose we want to create a variable called grades that is assigned as follows: Thus inner loop is executed N- times for every execution of Outer loop. When you nest two loops, the outer loop takes control of the number of complete repetitions of the inner loop. This can also be extended to include multiple conditions. Syntax of Nested for loop in R: The placing of one loop inside the body of another loop is called nesting.
(Notice that in the second ifelse statement only the first element in the series was computed.) s 10 H zeros(s) for c 1:s for r 1:s H(r,c) 1/(r+c-1) end end. Thus it is important to remember which logical operator to use in which situation. Whereas & (and) and | (or) apply element-wise to vectors, & and || apply to vectors of length one, and only evaluate their second argument in the sequence if necessary. The operators & and || are often used to denote multiple conditions in an if statement. R PROGRAMMING LANGUAGEUsing a for loop, write your own R function, evensum(data), that returns the sum of all the even values in the. The above expression reads: if condition on the data is true, then do the true value assigned otherwise execute the "false value." Ifelse(condition on data, true value returned, false returned) In R, one can write a conditional statement as follows: That is a bit abstract, so let's get our hands dirty. Commands may be grouped together in braces,, in which case the value of the group is the result of the last expression in the group evaluated. Even an assignment is an expression whose result is the value assigned, and it may be used wherever any expression may be used in particular multiple assignments are possible. R is an expression language in the sense that its only command type is a function or expression which returns a result. In this section we will explore some simple, yet powerful, programming tools in R, such as loops, if-then and while statements. One of the most powerful features of R is in being able to do programming, without a lot of the low-level detailed bookkeeping issues that one needs to keep track of in other computer programming languages like C, Java, Perl, etc. So far we have mainly used R for performing one-line commands on vectors or matrices of data. Programming Loops and If-then/for/while Statements