How to split dataset into 2/3 for training and 1/3 for testing include plot the graph?

This is my coding...but i got error and cannot get the correct answer.

can you guy help me...Pleaseeeee

clear all, close all, clc

load hald;  % Load Portlant Cement dataset
A = ingredients;
b = heat;

N=13; %number of row
idx=1:13;
PD=2/3;
%split data for training and testing
Ptrain=idx(1:round(PD*N));Ttrain=idx(1:round(PD*N));
Ptest=idx(round(PD*N)+1:end,:);Ttest=idx(round(PD*N)+1:end,:);

dataPTrain=hald(Ptrain);
dataPTest=hald(Ptest);

[U,S,V] = svd(A,'econ');

x = V*inv(S)*U'*b;                    % Solve Ax=b using the SVD

plot(dataPTrain,'k','LineWidth',2);  hold on            % Plot data
plot(dataPTest,'r-o','LineWidth',1.,'MarkerSize',2); % Plot regression
l1 = legend('Heat data','Regression')

%% Alternative 1  (regress)
x = regress(b,A);

%% Alternative 2  (pinv)
x = pinv(A)*b;

Answer 1

[Sulaymon Eshkabilov]

You should use random partition of your total data set, e.g.:

rng("default"); % For reproducibility
n = length(X);  %   
C = cvpartition(n, "HoldOut", 65);   % 65% for training and the remaining 35% for testing
INDEXtrain = training(C,1);
INDEXtest = ~ INDEXtrain;
X_test = X(INDEXtest,:);   
Y_test = Y(INDEXtest,:);
X_train = X(INDEXtrain,:); 
Y_train = Y(INDEXtrain,:);

[NOR AZIERA]

I still get the error...

Answer 2

[Voss]

This:

Ptest=idx(round(PD*N)+1:end,:);Ttest=idx(round(PD*N)+1:end,:)

should be this:

Ptest=idx(round(PD*N)+1:end);Ttest=idx(round(PD*N)+1:end)

because idx is a row vector, and the way you had it was trying to index beyond row 1 (the only row it has) of idx.

[NOR AZIERA]

sir...what the right coding for plot?

plot(dataTrain,'k','LineWidth',2); hold on % Plot data

plot(dataTest,'r-o','LineWidth',1.,'MarkerSize',2); % Plot regression

l1 = legend('Heat data','Regression')