Evaluation is the process of interpreting and carrying out the instructions in a computer program. In R, evaluation is performed by the R interpreter.
When a complete expression is entered at the prompt, it is evaluated and the result of the evaluated expression is returned. The result may be auto-printed. For example, the following code:
x <- 5
x
will assign the value 5 to the variable `x` and then print the value of `x` to the console.
The `print()` function can also be used to explicitly print the value of an object. For example, the following code:
x <- 5
print(x)
will also print the value of `x` to the console.
The numbers in the square brackets that are printed when an R vector is printed are not part of the vector itself. They are merely part of the printed output. This is done to make the output more friendly to the users.
It is important to understand the difference between the actual R object and the manner in which that R object is printed to the console. The printed output may have additional bells and whistles to make the output more friendly to the users. However, these bells and whistles are not inherently part of the object.
- The evaluation of an expression is performed in the current environment.
- The evaluation of an expression may depend on the values of other variables in the environment.
- The evaluation of an expression may also depend on the values of global variables.
Integer Sequences
The `:` operator is used to create integer sequences in R. For example, the following code:
x <- 1:10
will create a vector of integers from 1 to 10. The `:` operator can also be used to create sequences with gaps. For example, the following code:
x <- 2:10
will create a vector of integers from 2 to 10, skipping 1.
The `:` operator can also be used to create sequences with negative numbers. For example, the following code:
x <- -5:5
will create a vector of integers from -5 to 5.
The `:` operator is a very versatile operator that can be used to create a variety of integer sequences.
