# Revision of errors from Wed, 09/02/2009 - 08:07

Revisions allow you to track differences between multiple versions of your content, and revert back to older versions.

### General strategies for locating errors

• Use the traceback() function in R after an error occurs.It will print out the sequence of function calls that lead to the error.

### "Argument is missing, with no default"

• Variations include:
• Error in single.na(to) : argument is missing, with no default
• Typical cause: A leading or trailing comma in your code makes R think that you wanted to pass in a parameter, but left it empty (hence "missing, with not default")
• Examples:
to=c(,'x','y','z')
• trailing comma
mxMatrix("Name"
nrow=3,ncol=3,free=TRUE, values=.5,
)

• Cure: remove the errant comma

### Error in convertVFN(... NAs introduced by coercion

• Whenever you see NAs being introduced by coercion, suspect that you have the wrong type of value for a parameter: For instance, perhaps you are setting a number to string or vice versa... the coercion will fail, leaving an NA, which R warns you about.
• Example:
#You say:

    mxMatrix(type = "Full", nrow = 1, ncol = 1, free = FALSE,
values = "l1", labels = "aa",
lbound = 0, ubound = 2, name = "la"),


We try and convert the character "l1" to a numeric value, can't, return an NA... hence the error: NAs induced by coercion.

• The error:
    Warning messages:
1: In convertVFN(values, free, labels, lbound, ubound, nrow, ncol) :
NAs introduced by coercion...

• Solution: in this case, set the value to a numeric, (and remember that to equate values, you set the labels to be the same)