////////////////////////////////////
function double difv(double v1, double v2) {
  return abs(v1-v2);
}
target=1;
minv=1e307;
Loop(ii,1,wks.maxRows) {
  d=difv(col(1)[ii], target);
  if(d<minv) { minv=d; mini=ii; }
}
//// Output results /////
worksheet -a 3;
nc=wks.ncols;
wcol(nc-2)[C]$=Index;  wcol(nc-2)[1]=mini;
wcol(nc-1)[C]$=X;      wcol(nc-1)[1]=col(1)[$(mini)];
wcol(nc)[C]$=Y;        wcol(nc)[1]=col(2)[$(mini)];
////////////////////////////////////

quote:

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Originally posted by greg

Rather than the closest value, how about interpolating to get the estimated Y value at an exact X value?

range rax = [Book1]Sheet1!col(1);
range ray = [Book1]Sheet1!col(2);
range raxy = (rax,ray);
InterpolatedY = raxy(1);

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quote:

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Originally posted by greg

range raxy = (rax,ray) creates an XYRange out of rax (column 1) and ray (column 2) where rax is the 'x' and ray is the 'y'. I could interpolate the other way by using range rayx = (ray,rax).

InterpolatedY = raxy(1) finds the value of Y at X = 1 in the XYRange.

InterpolatedY is a scalar value, so:
col(3)=InterpolatedY
will not do anything unless you have set a data range for column 3. You could set a cell in column 3 with:
col(3)[1] = InterpolatedY

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