how to extract a specific data from struct formatted dataset

i have battery dataset in a struct format. i need to extract "capacity" data alone from the dataset. the capacity data is present under 'discharge' only.

here is the dataset structure

i used the following code

z = load('B0005.mat');
for i = 1:length(z.B0005.cycle)
    a(i) = z.B0005.cycle(i).data.Capacity;
end

the problem is, the first field('charge') does not contain 'capacity' data so it throws an error:

Reference to non-existent field 'Capacity'.
Error in Untitled (line 3)
a(i) = z.B0005.cycle(i).data.Capacity;

can anyone please tell me where iam going wrong and help me out in correcing the error. i want to read just the capacity data situated under discharge field

Answer 1

[per isakson]

Try this

%%
z = load('B0005.mat');
len = length(z.B0005.cycle);
a = zeros( len, 1 );
for ii = 1:len
    if strcmp( z.B0005.cycle(ii).type, 'discharge' ) 
        a(ii) = z.B0005.cycle(ii).data.Capacity;
    end
end

Every second value of a will be zero

[Padmamalini T H]

thanks a lot. this works perfecct

Answer 2

[Muthu]

I assume from the data and image that you have posted, the z.B0005.cycle(i) refers to 'charge' and 'discharge' which is placed consecutively: All 'discharge' in even and all 'charge' in odd indices.

Hence you can modify your code, so that you iterate only through your even indices.

for i = 1:length(z.B0005.cycle)
    if mod(i,2)==0
       a(i) = z.B0005.cycle(i).data.Capacity; 
    end
end

Hope this helps.

Good Luck.

[Padmamalini T H]

No the discharge data doesnt come in even indices. What i have shown is the initial recordings. After this there is no order and all charge and discharge recordings are random