When I create a dataframe from numeric vectors, R seems to truncate the value below the precision that I require in my analysis:
data.frame(x=0.99999996)
If you really want set up R to print its results with utterly unreasonable precision, then use: options(digits=16).
Note that this does nothing for that accuracy of functions using htese results. It merely changes how values appear when they are printed to the console. There is no rounding of the values as they are being stored or accessed unless you put in more significant digits than the abscissa can handle. The 'digits' option has no effect on the maximal precision of floating point numbers.