# How to interpolate this list of data

Can anyone help me to interpolate this list of data?

I try to use Interpolation function but think the number of points it's not enough.

Here I show the result using ListPlot: I want to interpolate beacuse I want the "y" for a specific value of "x".

List of data

• Which y do you want for x==.04? – Carl Woll Sep 19 '17 at 17:34
• Do you want a parametric interpolation (of the form $(x(s),y(s)$)? – anderstood Sep 19 '17 at 17:40
• Let supose the horizontal axes is "x" and the vertical is "y". I want a interpolation which gives me y(x). – Mateus Sep 19 '17 at 17:56
• Carl's question focuses on the fact that there is not a unique value for y[0.04]. In US lingo, we say the graph fails the Vertical Line Test and does not define y as a function of x. – Michael E2 Sep 19 '17 at 18:13
• Actually, I have my "y" and I want my "x" for this specific "y". – Mateus Sep 19 '17 at 18:17

data = Import["/Users/roberthanlon/Downloads/cD7ACXNZ.txt", "Table"];


As stated in the comments, your y is not a function of x since it is not single-valued. To form a single-valued function reverse the data point values, i.e., look at {y, x} rather than {x, y}.

data2 = Reverse /@ data;

f = Interpolation[data2];

{ymin, ymax} = MinMax[data2[[All, 1]]];

Plot[f[y], {y, ymin, ymax}, PlotRange -> All] • Thanks Rob Hanlon. Problem solved. – Mateus Sep 20 '17 at 17:44