# Count percentage of certain number in struct

2 views (last 30 days)
Nienke de Vries on 15 Feb 2024
Edited: Voss on 20 Feb 2024
I have a 1x120 struct with 11 fields. 1 of the fields contains the condition (half of which 0, and half 1) and another field contains the accuracy (either good=1 or wrong=0).
I now want to know how many 1s are in the accuracy field for condition=1. How do I do this? Which function will I need?
I have multiple of these 1x120 structs, so I don't want to count it manually.
Dyuman Joshi on 15 Feb 2024
nnz or sum with numel
Nienke de Vries on 15 Feb 2024
thanks!

Voss on 15 Feb 2024
% something similar to your 1x120 struct:
S = struct( ...
'condition',num2cell(logical(randi([0,1],1,120))), ...
'accuracy',num2cell(logical(randi([0,1],1,120))))
S = 1×120 struct array with fields:
condition accuracy
% number of elements of S with accuracy==1 and condition==1 (what you asked about)
n_good_condition_1 = nnz([S([S.condition]).accuracy])
n_good_condition_1 = 36
% number of elements of S with accuracy==1 and condition==0
n_good_condition_0 = nnz([S(~[S.condition]).accuracy])
n_good_condition_0 = 34
% number of elements of S with accuracy==0 and condition==1
n_wrong_condition_1 = nnz(~[S([S.condition]).accuracy])
n_wrong_condition_1 = 20
% number of elements of S with accuracy==0 and condition==0
n_wrong_condition_0 = nnz(~[S(~[S.condition]).accuracy])
n_wrong_condition_0 = 30
Nienke de Vries on 15 Feb 2024
Thank you so much for this extensive answer!!
Voss on 15 Feb 2024
Edited: Voss on 20 Feb 2024
You're welcome! Any questions, let me know.

Adam Danz on 15 Feb 2024
Edited: Adam Danz on 15 Feb 2024
Looks like @Voss hit the nail on the head.
Another approach is to use groupcounts to tally the counts between the two groups.
1. Convert the structure to a table. I'll use Voss's struct example.
S = struct( ...
'condition',num2cell(logical(randi([0,1],1,120))), ...
'accuracy',num2cell(logical(randi([0,1],1,120))));
T = struct2table(S);
head(T) % show some rows of the table
condition accuracy _________ ________ false false true false false true true false true false false false false true false true
2. Apply groupcounts
summaryTable = groupcounts(T,{'condition','accuracy'})
summaryTable = 4×4 table
condition accuracy GroupCount Percent _________ ________ __________ _______ false false 32 26.667 false true 38 31.667 true false 27 22.5 true true 23 19.167

Austin M. Weber on 15 Feb 2024
You can use nnz which tells you how many non-zeros are in an array. If your struct is named s then you can extract the data you want and perform the calculations:
idx = s.Condition == 1; % Find positions where the condition = 1
accuracy = s.Accuracy(idx); % Find the accuracy values where the condition = 1
number_of_ones = nnz(accuracy); % Count number of ones in 'accuracy'
Austin M. Weber on 15 Feb 2024
@Voss Thank you for the clarification!
Voss on 15 Feb 2024
@Austin M Weber You're welcome!

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