How to select specific legend entries for bar chart

I have written a code to produce a bar chart of results. The results have been calculated using 4 different methods and that is how I have coloured the bars. How do I create a legend with just the four colours I have chosen? Instead I can only get the first four entries in the chart, where three of them are the same colour:

      % The code is as follows:
  figure('name','Extraction energy analysis');
  set(gca,'YScale','log')

hold on
    for i=1:n
     xlabel('Resource')       
     h=bar(i,output_Q_r(i));
    if extraction(i) == 0
        set(h,'FaceColor','g');
    elseif extraction(i) == 1
        set(h,'FaceColor','b');
    elseif extraction(i) == 2
        set(h,'FaceColor','y');
    elseif extraction(i) == 3
        set(h,'FaceColor','r');
    end
    end

      hold off
  set(gca,'xticklabel',resource)
  ylabel('Energy (kW)')
  X=(1:16);
  XTickLabel=resource;
  set(gca,'XTick',X)     %assigning number of ticks to number of labels as automatically reaches limit of 15
  title(char({'Energy required to extract 1000T of each resource',' from lunar south pole soil in 1 year'}))
  xticklabel_rotate([],45)
  legend('Thermal gas release',char({'hydrogen reduction',' of ilmenite'}),char({'electrolysis of',' molten regolith'}),'other')  
    end

Answer 1

[Rik]

You can compile a vector of handles and use that as the pointer for legend

h_list=[];
hold on
  for i=1:n
   xlabel('Resource')       
   h=bar(i,output_Q_r(i));
  if extraction(i) == 0
      set(h,'FaceColor','g');
      h_list(extraction(i)+1)=h;
  elseif extraction(i) == 1
      set(h,'FaceColor','b');
      h_list(extraction(i)+1)=h;
  elseif extraction(i) == 2
      set(h,'FaceColor','y');
      h_list(extraction(i)+1)=h;
  elseif extraction(i) == 3
      set(h,'FaceColor','r');
      h_list(extraction(i)+1)=h;
  end
  end
  hold off
set(gca,'xticklabel',resource)
ylabel('Energy (kW)')
X=(1:16);
XTickLabel=resource;
set(gca,'XTick',X)     %assigning number of ticks to number of labels as automatically reaches limit of 15
title(char({'Energy required to extract 1000T of each resource',' from lunar south pole soil in 1 year'}))
xticklabel_rotate([],45)
legend(h_list,'Thermal gas release',char({'hydrogen reduction',' of ilmenite'}),char({'electrolysis of',' molten regolith'}),'other')  
end

[Hannah Sargeant]

That's great! Thank you very much

Answer 2

[Tiago Dias]

Hi, what is extraction?