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How to plot XScale in log in boxplot? I used set(gca,'XScale','log') but the scale width are unequal. Kindly help.

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Swathi S
Swathi S on 11 Jun 2021
Answered: Asvin Kumar on 23 Jun 2021
I want the xscale to appear as below from 10^-1 to 10^1 with equal spacing but unable to achieve it with the following code.
CODE:
clear all;
close all;
C0p1 = [91.57 89.96 86.61]'; %for 0.1m transmission distance 10, 150, 1000 mS/m
C0p2=[78.42 75.22 68.51]';
C0p3 = [68.76 63.95 53.89]';
C0p4=[61.3 54.89 41.48]';
C0p5 = [55.25 47.23 30.47]';
C0p6=[50.15 40.52 20.41]'
C0p7=[45.73 34.5 11.03]'
C0p8=[41.81 28.97 2.156]'
C0p9=[38.28 23.84 -6.326]'
C1 = [35.0707 19.0265 -14.495]'; %No need to change 1 to 5
C2=[12.1437 -19.9448 -86.9877]';
C3 = [-3.3613 -51.4904 -152.0584]';
C4=[-15.8081 -79.9851 -214.071]';
C5 = [-26.5764 -106.7977 -274.405]';
C6=[-36.28 -132.5 -333.7]'
C7=[-45.25 -157.6 -392.2]'
C8=[-53.69 -182 -450.2]'
C9=[-61.72 -206.1 -507.8]'
C10=[-69.42 -229.9 -565.1]'
group = [ ones(size(C0p1));
2 * ones(size(C0p2));
3 * ones(size(C0p3))
4 * ones(size(C0p4))
5 * ones(size(C0p5))
6 * ones(size(C0p6));
7 * ones(size(C0p7))
8 * ones(size(C0p8))
9 * ones(size(C0p9))
10 * ones(size(C1));
11 * ones(size(C2));
12 * ones(size(C3))
13 * ones(size(C4))
14 * ones(size(C5))
15 * ones(size(C6));
16 * ones(size(C7))
17 * ones(size(C8))
18 * ones(size(C9))
19 * ones(size(C10))];
group = repelem((1:19)',[numel(C0p1);numel(C0p2);numel(C0p3);numel(C0p4);numel(C0p5);numel(C0p6);numel(C0p7);numel(C0p8);numel(C0p9);numel(C1);numel(C2);numel(C3);numel(C4);numel(C5);numel(C6);numel(C7);numel(C8);numel(C9);numel(C10)]);
h1=boxplot([C0p1; C0p2; C0p3; C0p4; C0p5; C0p6; C0p7; C0p8; C0p9; C1; C2; C3; C4; C5; C6; C7; C8; C9; C10],group,'colors','g','widths',0.25,'BoxStyle','filled')
set(gca,'XTickLabel',{'0.1', '0.2', '0.3', '0.4', '0.5', '0.6', '0.7', '0.8', '0.9', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10'})
lines = findobj(h1, 'type', 'line', 'Tag', 'Median');
set(lines, 'Color', 'R');
------------------------------------------
For: set(gca,'XTickLabel',{'0.1', '0.2', '0.3', '0.4', '0.5', '0.6', '0.7', '0.8', '0.9', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10'})
Output is:
For: set(gca,'XScale','log')
Output is:
For: set(gca,'Xtick',-1:1); %// adjust manually; values in log scale
set(gca,'Xticklabel',10.^get(gca,'Xtick'));
Output is:

Answers (1)

Asvin Kumar
Asvin Kumar on 23 Jun 2021
You were right to set the 'XScale' axes property to 'log'. The reason it didn't behave as expected was becasuse the positions of each box in the boxplot were 1:19 by default. You can modify that by using the 'Position' Name-Value pair. Here's an updated version of the code.
C0p1 = [91.57 89.96 86.61]'; %for 0.1m transmission distance 10, 150, 1000 mS/m
C0p2=[78.42 75.22 68.51]';
C0p3 = [68.76 63.95 53.89]';
C0p4=[61.3 54.89 41.48]';
C0p5 = [55.25 47.23 30.47]';
C0p6=[50.15 40.52 20.41]';
C0p7=[45.73 34.5 11.03]';
C0p8=[41.81 28.97 2.156]';
C0p9=[38.28 23.84 -6.326]';
C1 = [35.0707 19.0265 -14.495]'; %No need to change 1 to 5
C2=[12.1437 -19.9448 -86.9877]';
C3 = [-3.3613 -51.4904 -152.0584]';
C4=[-15.8081 -79.9851 -214.071]';
C5 = [-26.5764 -106.7977 -274.405]';
C6=[-36.28 -132.5 -333.7]';
C7=[-45.25 -157.6 -392.2]';
C8=[-53.69 -182 -450.2]';
C9=[-61.72 -206.1 -507.8]';
C10=[-69.42 -229.9 -565.1]';
pos = [0.1:0.1:0.9 1:10];
group = repelem((pos)', ... % updated the group numbers
[numel(C0p1);numel(C0p2);numel(C0p3);numel(C0p4);numel(C0p5);...
numel(C0p6);numel(C0p7);numel(C0p8);numel(C0p9);numel(C1);numel(C2);...
numel(C3);numel(C4);numel(C5);numel(C6);numel(C7);numel(C8);numel(C9);...
numel(C10)]);
x = [C0p1; C0p2; C0p3; C0p4; C0p5; C0p6; C0p7; C0p8; C0p9; C1; C2; C3; C4; ...
C5; C6; C7; C8; C9; C10];
h1=boxplot(x,group,'colors','g','widths',0.25,...
'BoxStyle','filled','Positions',pos); % updated positions
lines = findobj(h1, 'type', 'line', 'Tag', 'Median');
set(lines, 'Color', 'R');
grid on;
ax = gca;
ax.XScale ='log';
ax.XTickLabelMode = 'auto'; % optional
ax.XTickMode = 'auto'; % optional
Warning: Negative limits ignored
You will notice that the code throws a warning. This warning is because the position of the Median of the first bar plot has negative values which cannot be converted to a log scale.
You will also notice that the markers have a decreasing length from left to right. This is also because of the conversion from a linear to a log scale. All Median lines have the same length in the linear scale but it looks different in the log scale. This can be fixed by updating the 'XData' property of all lines with the 'Median' tag.

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