Loop (or iteration) evaluates an expression repeatedly by either iterating over a vector (for
) or checking whether a condition is violated (while).
Such language constructs largely reduce the redundancy of the code if the same task is run over and over again each time with some changes in input.
The for
loop evaluates an expression by iterating over a given vector or list. The syntax of a for
loop is as follows:
for (var in vector) { expr }
Then, expr
will be evaluated iteratively, with var
taking the value of each element of vector
in turn. If vector
has n
elements, then the preceding loop is equivalent to evaluating:
var <- vector[[1]] expr var <- vector[[2]] expr ... var <- vector[[n]] expr
For example, we can create a loop to iterate over 1:3
with iterator variable i
. In each iteration, we will show text on the screen to indicate the value of i
:
for (i in 1:3) { cat("The value of...