I have code which outputs numbers, for example,(0.2945847, 0.8647834, 1.6*10^-6) and similar. I would like to take these numbers and round them to 4 significant figures, but I can't find a way to do this.
I know N[expr, digits] can round an expression to certain significant figures but it doesn't seem to work with my numbers.
Below is the function I use for rounding to p significant figures. I played around with a few methods, but settled on MantissaExponent on the philosophy of using built-in functions whenever possible.
NTo[x_?Internal`RealValuedNumericQ, p_Integer?Positive] :=
Function[{m, e}, N[Round[m 10^p]10^(e - p)]] @@ MantissaExponent[x];
NTo[z_?NumericQ, p_Integer?Positive] := Complex[NTo[Re[z], p], NTo[Im[z], p]];
NTo[p_Integer?Positive][x_] := NTo[x, p];
Example usage:
NTo[4] /@ {0.2945847, 0.8647834, 1.6*10^-6}
(* {0.2946, 0.8648, 1.6*10^-6} *)
N is implemented such it will never lose precision when the input is already a floating point number (with more significant digits than the second argument of N).
In order to enforce rounding to 4 digits, use SetPrecision:
a = {0.2945847, 0.8647834, 1.6*10^-6};
SetPrecision[a, 4]
{0.2946, 0.8648, 1.600*10^-6}
NsigFig[x_, digits_] :=
If[x == 0, 0., Round[x, 0. + 10^(Round[Log[10, x] - digits + 0.5])]]
Try:
NsigFig[3.1415926, 4]
(* 3.142 *)
NumberForm. – Sumit Aug 06 '18 at 13:31