The debug() function in R allows you to step through the execution of a function, line by line. This can be helpful for debugging errors in your code.
To use debug(), you first need to flag the function that you want to debug. This is done by calling the debug() function with the name of the function as the argument. For example, to flag the lm() function, you would use the following code:
debug(lm)
Once you have flagged a function, you can call it as usual. However, instead of executing the function normally, R will enter the debugger at the first line of the function body. From there, you can step through each expression in the body one at a time.
There are a few special commands that you can use in the debugger:
- `n` executes the current expression and moves to the next expression.
- `c` continues execution of the function and does not stop until either an error or the function exits.
- `Q` quits the debugger.
For example, if you wanted to debug the first line of the lm() function, you would use the following code:
debug(lm)
lm(y ~ x)
Browse[2]> n
debug: ret.x <- x
This would cause R to enter the debugger at the first line of the lm() function, which is the line that assigns the value of x to the variable ret.x. From there, you could use the `n` command to step through the next expression, which is the line that assigns the value of y to the variable ret.y.
You can continue stepping through the expressions in the lm() function until you reach the line where the error is occurring. Once you have found the line where the error is occurring, you can use the `c` command to continue execution of the function and see what happens.
To turn off interactive debugging, you can use the undebug() function. For example, to turn off interactive debugging for the lm() function, you would use the following code:
undebug(lm)
Once you have turned off interactive debugging, R will no longer enter the debugger when you call the lm() function.
