MATLAB: What is the solution for “Error using griddedInterpolant The grid vectors must contain unique points.”

MATLAB: What is the solution for “Error using griddedInterpolant The grid vectors must contain unique points.”

interpolation

Hi,
I need to interpolate the data of 243 frame into 51 frame which 0 to 100%. However, the result shows
“Error using griddedInterpolant The grid vectors must contain unique points.”
I’m not sure how to solve the error and what is the meaning of unique points.
``X=xlsread('JRF DATA 10DEG.xlsx',1,'J4:M243');% Make original dataoldPcntValsx = X(:,1) ;oldXvals = X(:,2) ;% Set a new spacing from 0 to 1 and interpolatenewPcntValsx = 0:2:100;newXvals = interp1(oldPcntValsx, oldXvals, newPcntValsx);newX = newXvals(:);% Make original dataoldPcntValsy = X(:,1) ;oldYvals = X(:,3) ;% Set a new spacing from 0 to 1 and interpolatenewPcntValsy = 0:2:100;newYvals = interp1(oldPcntValsy, oldYvals, newPcntValsy);newY =newYvals(:);% Make original dataoldPcntValsz = X(:,1) ;oldZvals = X(:,4) ;% Set a new spacing from 0 to 1 and interpolatenewPcntValsz = 0:2:100;newZvals = interp1(oldPcntValsz, oldZvals, newPcntValsz);newZ = newZvals(:);N2 = [newX,newY,newZ];``