R: Transformation of data with log10 qqline warning message the condition has length > 1 and only the first element will be used

Question

I want to transform my data in R with a logarithm and want to plot it with a qqplot. I got the warning message, see below. What does this exactly mean for the plot?

log <-log10(life$p) 
qqplot(life$p,log, main = "Normal Q-Q Plot",plot.it = TRUE)
qqline(life$p,log, col="red")

The warning message was:

In if (datax) { :
the condition has length > 1 and only the first element will be used

Answer 1

There seem to be several things wrong here.

Your call to qqplot is almost certainly not doing what you wanted. Notice that the documentation ?qqplot says:

qqplot produces a QQ plot of two datasets.

Your code is:
qqplot(life$p,log, main = "Normal QQ Plot",plot.it = TRUE)
The "two datasets" that you are giving it are life$p and log, so this will plot the quantiles of life$p against the quantiles of log = log10(life$p). That makes no sense. Since your title says "Normal QQ Plot", I suspect that you wanted to plot log against a Normal distribution. To get that, you probably wanted:
qqnorm(log, main = "Normal QQ Plot")

Now to your error message.
The documentation for qqline gives the argument sequence as:

qqline(y, datax = FALSE, distribution = qnorm,
       probs = c(0.25, 0.75), qtype = 7, ...)

Your call to this function is:

qqline(life$p,log, col="red")

You don't name the arguments so they are interpreted in order. life$p is y and log is datax. datax is supposed to be a logical value (TRUE/FALSE), but you are passing it an array of numbers, hence the error message. I believe that what you intended was:

qqline(log, col="red")

Finally, log is the name of the natural logarithm function. It is a bad idea to name your variable log since it will be confusing if that refers to the function or the variable.