In this example I used appendTo.
f[x_] := x + 1;data = {};For[x = 1, x <= 10, x++,f[x];spec = AppendTo[data, {x, f[x]}]] // Timing // First
Out[37]= 0.000054
ListPlot[spec]
In this example I used appendTo.
f[x_] := x + 1;data = {};For[x = 1, x <= 10, x++,f[x];spec = AppendTo[data, {x, f[x]}]] // Timing // First
Out[37]= 0.000054
ListPlot[spec]