Debugging
Computing for Data Analysis
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Something’s Wrong!
Indications that something’s not right
message: A generic notification/diagnostic message produced by the message
function; execution of the function continues
warning: An indication that something is wrong but not necessarily fatal;
execution of the function continues; generated by the warning function
error: An indication that a fatal problem has occurred; execution stops;
produced by the stop function
condition: A generic concept for indicating that something unexpected can
occur; programmers can create their own conditions
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Something’s Wrong!
Warning
> log(-1)
[1] NaN
Warning message:
In log(-1) : NaNs produced
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Something’s Wrong
printmessage <- function(x) {
if(x > 0)
print("x is greater than zero")
else
print("x is less than or equal to zero")
invisible(x)
}
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Something’s Wrong
printmessage <- function(x) {
if(x > 0)
print("x is greater than zero")
else
print("x is less than or equal to zero")
invisible(x)
}
> printmessage(1)
[1] "x is greater than zero"
> printmessage(NA)
Error in if (x > 0) { : missing value where TRUE/FALSE needed
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Something’s Wrong!
printmessage2 <- function(x) {
if(is.na(x))
print("x is a missing value!")
else if(x > 0)
print("x is greater than zero")
else
print("x is less than or equal to zero")
invisible(x)
}
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Something’s Wrong!
printmessage2 <- function(x) {
if(is.na(x))
print("x is a missing value!")
else if(x > 0)
print("x is greater than zero")
else
print("x is less than or equal to zero")
invisible(x)
}
> x <- log(-1)
Warning message:
In log(-1) : NaNs produced
> printmessage2(x)
[1] "x is a missing value!"
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