# Create a new table from a plot constructed from data points

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aroj bhattarai on 17 Jan 2022
Edited: aroj bhattarai on 16 Feb 2022
Dear all,
Reading an excel sheet with around 24000 data points, I made a plot. Now I would like to create a new table from this plot with a user-defined interval, let say with only 10 data points. Is it possible to do so in Matlab?
Many thanks in advance.
Bhattarai

Voss on 17 Jan 2022
% a table with 1000 rows:
t = table((1:1000).',2*(1:1000).'+100,'VariableNames',{'x' 'y'})
t = 1000×2 table
x y __ ___ 1 102 2 104 3 106 4 108 5 110 6 112 7 114 8 116 9 118 10 120 11 122 12 124 13 126 14 128 15 130 16 132
% user-defined interval over x:
x_limits = [200 209];
% logical index saying whether each x in the table is within the interval:
idx = t.x >= x_limits(1) & t.x <= x_limits(2);
% new table with x and y but only where x is within the interval:
new_t = table(t.x(idx),t.y(idx),'VariableNames',{'x' 'y'})
new_t = 10×2 table
x y ___ ___ 200 500 201 502 202 504 203 506 204 508 205 510 206 512 207 514 208 516 209 518
##### 1 CommentShowHide None
aroj bhattarai on 18 Jan 2022
Thank you Benjamin for your interest on my question. But I guess my writing confused you for my objective. Your answer seems to extract specific (X,Y) data points from the given lumpsum data points and to create a new table out of it.
However, my objective is different. As shown in the attached figure A), I have a plot constructed from around 24000 (X,Y) data points where X runs from 1.0 to 1.3987 with data values as:
1.0000, 1.0236, 1.0256, 1.0287, ........, 1.0358, 1.0359, ....., 1.0579, 1.0581, 1.0596, 1.6113, .............., 1.3726, 1.3862, 1.3889, 1.3961, 1.3987.
As shown in figure B), my objective is to assign a user-defined interval/gap/step/space, for example 0.05 in the linear space of X data points in the plot. And from the plot, I would like to extract only 9 (X,Y) data points to be written in a new table, i.e., (1.00, Y1), (1.05, Y2), (1.10, Y3), (1.15, Y4), (1.20, Y5), (1.25, Y6), (1.30, Y7), (1.35, Y8), (1.3987, Y9).
Bhattarai

aroj bhattarai on 16 Feb 2022
Edited: aroj bhattarai on 16 Feb 2022
Although non-profesionally coded, sharing the desired answer in case somebody new in MATLAB have similar issue:
Reading the data set from the excel file
[~, ~, raw] = xlsread('C:\Users...\ABC.xlsx','PQR'); % read PQR sheet of ABC excel file
raw(cellfun(@(x) ~isempty(x) && isnumeric(x) && isnan(x),raw)) = {''};
cellVectors = raw(:,[1,11]);
raw = raw(:,[1,2,3,4,5,6,7,8,9,10,11]);
% 8th and 10th column are input X and Y dataset with X = [1.0 1.3987]
Laminp = data(:,8);
Siginp = data(:,10);
Tabulating the dataset
v = table;
llim=1;
ulim=24000;
v.lam = Laminp(1:24000);
v.sig = Siginp(1:24000);
clearvars data raw cellVectors R Laminp Siginp;
lamint(:,1) = v.lam;
Sigint(:,1) = v.sig;
Interpolating the dataset at desired X interval
t = table;
t.lamtab = lamint(:,1); % data acquired from another excel file tabulated in new table t
t.Sigtab = Sigint(:,1);
Lam_coarse = linspace(1, 1.3987, 10); % Coarse X dataset
Sig_coarse = interp1(t.lamtab,t.Sigtab,Lam_course); % Coarse Y dataset
xlswrite('C:\Users...\XYZ.xlsx',Lam_coarse','Data','A1'); % in the 1st column of Data sheet
xlswrite('C:\Users...\XYZ.xlsx',Sig_coarse','Data','B1'); % in the 2nd column of Data sheet
Plotting
figure(1)
plot(lamint(:,1),Sigint(:,1),'o','LineWidth',1.0, 'color','b');
hold on
plot(Lam_coarse,Sig_coarse,'-','LineWidth',1.0, 'color','b');
grid on
hold off

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