If statement: if none of doubles~= X then change the value of X to the closest to X...

I am designing a GUI to plot data on a user chosen time interval. I have a double 100x1 of datenum values which are not uniformly spaced. When user inputs a start time and there is no such double value I would like to have an if statement which will replace the start time with the closest there is to the inputted time. I would like to know if there is such a function ''if none such value found''? Thanks for help! (I presume isempty() doesn't work since my input is not an array and always has some values in it)

Answer 1

[Walter Roberson]

One step: interp1 with 'nearest'

But also very reasonable:

[~, idx] = min(abs(Times - entered_time))
Times(idx)