Selecting two data points form plot

clear all;

%% Loading the data and assigning the variable
load('_  Mix 0% .mat')
X1=x{1,1};
R1=r{1,1};
P1=phi{1,1};

%% Plotting
figure(1)
subplot(2,1,1)  
plot(X1,R1,'LineWidth',2)
subplot(2,1,2)  
plot(X1,P1,'LineWidth',2)

%% Selecting the range of data from X1 through clicking the plot using mouse
%[rx,ry]=ginput(2);
[xi,yi] = getpts(X1)
idx1=find(X1==rx(1));

My plot looks like above. I would like to truncate the vector such that is contains values from 300 to 600. where as in X1 doesn't contain 300 instead it has 300.2454 . I would like to write a genralized code where I can click on plot to record two data points from X1 (xdata).

[x,y] = getinput(2) returned vales are not from the vector i plotted.

[x,y] = getpts(X1) it is returning vector full of zeros. It should work occording to the manual.

rect = getrect(X1) This one also not working

Somebody please help me.