How can I plot only certain values from an array?

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

Answer 1

[Adam]

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]

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')

Answer 2

[Sudharsana Iyengar]

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.

Answer 3

[Ankit Jain]

Above all method are only applicable if the value to be plotted is same, what about if one wants varied values to be plotted?