How do I highlight a certain area between two lines?

I'm trying to graph measured CO2 levels compared to the safe range according to the WHO.

But when I use the patch command, but that highlights the ENTIRE area, and not the the area that crosses the high concentration.

[KSSV]

You need to pick the coordinates wisely to hightlight the region you want.

[Ben van Zon]

I'm not really sure how to do that, I'm not the greatest with this and the documentation with the patch command only specifies polygons.

[KSSV]

Attach your data and show us what region you want to highlight.

[Ben van Zon]

I attached the xlsx file, only need the data with the CO2 values, so row 11.

And I want to highlight the circled area

So the part where the concentration goes above the specified limit of 1000 ppm

Answer 1

[Star Strider]

The ‘Time’ format makes absolutely no sense to me, and readmatrix returns NaN for that column, so the posted code image will not work to convert it.

The ‘t’ and ‘CO2’ vectors need to be interpolated to a finer resolution than in the initial file for this to work correctly. Then, just use logical indexing to define the appropriate regions —

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1239957/DataTest2.xlsx', 'VariableNamingRule','preserve')

T1 = 346×13 table
    PM1.0    PM2.5    PM10    NO2    C2H5CH    VOC    CO    Temp     Press    Humi     CO2                  Time                 i 
    _____    _____    ____    ___    ______    ___    __    _____    _____    ____    ______    _____________________________    __

      0        0       0      391      83      243    58    22.27    73145     70     912.31    {'2022:41:12/20/22:16:41:15'}     0
      0        0       0      392      83      243    59    22.27    73145     70     911.64    {'2022:41:12/20/22:16:41:26'}     1
      0        0       0      391      83      243    59    22.27    73145     70     911.57    {'2022:41:12/20/22:16:41:37'}     2
      0        0       0      391      83      243    59    22.27    73145     70     911.15    {'2022:41:12/20/22:16:41:48'}     3
      0        0       0      392      83      244    60    22.27    73145     70     910.73    {'2022:41:12/20/22:16:41:59'}     4
      0        0       0      392      83      244    59    22.27    73145     70     908.55    {'2022:42:12/20/22:16:42:10'}     5
      0        0       0      392      82      244    60    22.27    73145     70     906.42    {'2022:42:12/20/22:16:42:21'}     6
      0        0       0      392      83      244    60    22.27    73145     70     905.56    {'2022:42:12/20/22:16:42:32'}     7
      0        0       0      392      83      244    60    22.27    73145     70     904.37    {'2022:42:12/20/22:16:42:43'}     8
      0        0       0      392      83      244    59    22.27    73145     70      907.3    {'2022:42:12/20/22:16:42:54'}     9
      0        0       0      391      82      243    60    22.27    73145     70     960.94    {'2022:43:12/20/22:16:43:05'}    10
      0        0       0      392      83      243    60    22.27    73145     70     976.15    {'2022:43:12/20/22:16:43:16'}    11
      0        0       0      391      82      244    60    22.27    73145     70     978.85    {'2022:43:12/20/22:16:43:27'}    12
      0        0       0      392      82      244    60    22.27    73145     70      971.3    {'2022:43:12/20/22:16:43:38'}    13
      0        0       0      392      83      244    60    22.27    73145     70     965.23    {'2022:43:12/20/22:16:43:49'}    14
      0        0       0      392      82      244    60    22.27    73145     70      956.8    {'2022:44:12/20/22:16:44:00'}    15

L = size(T1,1);
t = linspace(0, L-1, L).';
tv = linspace(min(t), max(t), 10*L);                    % Increase Resolution
CO2 = T1.CO2;
CO2v = interp1(t, CO2, tv);                             % Increase Resolution
SafeRange = [400 1000];
LvLo = CO2v >= SafeRange(1);                            % Logical Vector
LvHi = CO2v <= SafeRange(2);                            % Logical Vector
v1 = ones(size(t));
v1v = ones(size(tv));

figure
plot(tv, CO2v)
hold on
plot(tv(~LvHi), CO2v(~LvHi), 'r')
patch([tv(~LvHi) flip(tv(~LvHi))], [CO2v(~LvHi) SafeRange(2)*flip(v1v(~LvHi))], 'r')
hold off
ylim([0 1200])
yline(SafeRange, '-k', 'DisplayName','Safe Range')

.

Answer 2

[Chunru]

% Generate some data
t = 0:.1:10;
y = sin(t);

plot(t, y);
hold on
% highlight a portion of data
idx = t>6 & t<9;
area(t(idx), y(idx))

Answer 3

[Image Analyst]

This is a FAQ, so see the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_do_I_shade_the_region_between_two_curves?