# How can I plot only certain values from an array?

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Ahsan Khan on 17 Dec 2014
Answered: Ankit Jain on 21 Apr 2017
hi there, say I have an array [1,3,5,7,1,5,1,7,8,1]. I want to plot ONLY say value 1 from this array in accordance with the index in which the value resides in. so for the above array I want to plot for only value 1 occurrence: the value 1 shows up on index (0,4,6,and 9) so the plot will have an x-axis 1-10 and will only show a spike in the y direction when there is a value of 1 in the array. I have attached a an image as to what the result should look like. please help. thank you in advance. SN

Edited: Adam on 17 Dec 2014
a = [1,3,5,7,1,5,1,7,8,1];
idx = find( a == 1 );
figure; hAxes = gca;
stem( hAxes, idx, ones(numel(idx)) );
xlim( hAxes, [1 10] );
If you want to see the spikes more clearly you can also add e.g.
ylim( hAxes, [0 2] );
Thorsten on 17 Dec 2014
Edited: Thorsten on 17 Dec 2014
Or as a one-liner :-)
stem(find(a==1), ones(numel(find(a==1))), 'k', 'Marker','None', 'LineWidth', 3), box off, axis([0 12 0 2])
and if you want just dots, use plot instead of stem:
plot(find(a==1), ones(numel(find(a==1))), 'ko', 'MarkerSize', 6, 'MarkerFaceColor', 'k')

Sudharsana Iyengar on 17 Dec 2014
just another method. This is round about way and will actually take more time to execute.
j=1;
for i=1:length(a)
if a(i)==1
b(j,1)=i;
b(j,2)=1;
j=j+1;
end
end
plot (b(:,1),b(;,2))
This will store the values of i for which the value is equal to 1. Which you can plot.

Ankit Jain on 21 Apr 2017
Above all method are only applicable if the value to be plotted is same, what about if one wants varied values to be plotted?