Switch skipping over cases in new loop

Evening everyone,

I have a strange problem. In the code below, switch is recongising all conditoins in respect to "qq" within its loop and changing the variable value accordingly. However, the second switch "pp" it will only recongise the condition for the first loop only, after which the same variable is used i.e., it assesses the cases and skips over them. I have tried changing the case brackets from { } to ( ), clearing the counter (pp) to force it reload the variable in respect to the "i" loop and deleting the variable itself. None of this is working and I am stumped.

I do not have any data to provide because it is too large. Any ideas?

Thanks

for i=1:numel(H) % 9 figures
                    ax=findobj(H(i),'Type','axes');
                    for j=1:numel(ax)
                        
                        leg_tit_up = sprintf('Slope: %s%s',SA_type,char(176));
                        
                        % Nasty fix
                        qq = i; % Changed to qq to try and get second switch working
                        switch(qq)
                            case{1,4,7}
                                cell_trans_idx = cell_trans_flip{1};
                            case{2,5,8}
                                cell_trans_idx = cell_trans_flip{2};
                            case{3,6,9}
                                cell_trans_idx = cell_trans_flip{3};       
                        end
                        %clear switch
                        clear qq;
                        pp = i; % Only works after one conditon then bypasses to end - keeping the initial "leg_tit_dwn" value
                        switch(pp)
                            case{pp>7}
                                leg_tit_dwn =Water_levels(1) ;
                            case{pp>3 && pp<7}
                                leg_tit_dwn =Water_levels(2) ;
                            case{pp<4}
                                leg_tit_dwn =Water_levels(3) ;
                        end
                        clear pp
                        %clear switch


                        leg_tit = {leg_tit_up;leg_tit_dwn};
                        
                        lgd = legend(ax(j),Cell_ID(cell_trans_idx),'fontweight','bold','box','on','location','bestoutside');
                        title(lgd,leg_tit);
                        clear leg_tit_dwn;
                    end
                end

Answer 1

[Walter Roberson]

You have

                        pp = i; % Only works after one conditon then bypasses to end - keeping the initial "leg_tit_dwn" value
                        switch(pp)
                            case{pp>7}
                                leg_tit_dwn =Water_levels(1) ;
                            case{pp>3 && pp<7}
                                leg_tit_dwn =Water_levels(2) ;
                            case{pp<4}
                                leg_tit_dwn =Water_levels(3) ;
                        end

That code is effectively

if ismember(pp, [pp>7])
    leg_tit_dwn =Water_levels(1) ;
elseif ismember(pp, [pp>3 && pp<7])
    leg_tit_dwn =Water_levels(2) ;
elseif ismember(pp, [pp<4])
    leg_tit_dwn =Water_levels(3) ;
end

Notice this can only be true if pp is 0 or 1.

If you must use switch() instead of if/elseif, then change the

switch(pp)

to

switch(true)

and then you would be doing the equivalent if ismember(true, pp>7) which is at least possible.

[Walter Roberson]

Question: why do you permit pp>3 and pp<4 to overlap ? For example if pp is 3.1 then it is both > 3 and < 4 so a reader would be justified in having confusion over which value applies.

[DGM]

Also, pp=7 is a case which is not handled at all.

Answer 2

[DGM]

That's not how switch-case statements work. The case is only entered when the switch expression (pp is numeric) is equal to the case expression (which are logical). Just use if-else structures here.

% simplified for demonstration
i = 5

switch i
    case {1,4,7}
        cell_trans_idx = 1
    case {2,5,8}
        cell_trans_idx = 2
    case {3,6,9}
        cell_trans_idx = 3
end

% what happens when i = 7?
if i>7
    leg_tit_dwn = 1
elseif i>3 && i<7
    leg_tit_dwn = 2
elseif i<4
    leg_tit_dwn = 3
end