Count percentage of certain number in struct

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]

nnz or sum with numel

[Nienke de Vries]

thanks!

Answer 1

[Voss]

% 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]

Thank you so much for this extensive answer!!

[Voss]

You're welcome! Any questions, let me know.

Answer 2

[Adam Danz]

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 

Answer 3

[Austin M. Weber]

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'

[Voss]

That code is appropriate for a scalar struct whose fields are of size 1x120:

s = struct('Accuracy',randi([0,1],1,120),'Condition',randi([0,1],1,120))

s = struct with fields:
     Accuracy: [0 0 0 0 0 0 1 0 1 1 0 1 1 1 1 0 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 0 1 1 0 0 1 1 1 1 0 0 0 0 0 0 0 0 1 0 1 0 0 0 1 0 1 1 0 1 0 1 1 0 1 0 1 1 0 1 0 0 1 1 1 1 1 0 1 0 0 1 … ] (1×120 double)
    Condition: [1 1 1 0 1 0 1 1 0 1 1 1 0 1 0 1 0 0 0 1 0 0 1 0 1 1 1 1 1 0 0 1 1 1 0 1 0 0 0 1 1 1 0 0 1 1 1 0 0 1 0 1 0 1 0 1 1 0 0 0 0 1 0 0 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 0 0 0 … ] (1×120 double)

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'

number_of_ones = 31

but the question asks about a 1x120 struct:

s = struct('Accuracy',num2cell(randi([0,1],1,120)),'Condition',num2cell(randi([0,1],1,120)))

s = 1×120 struct array with fields:
    Accuracy
    Condition

in which case the syntax is different:

idx = [s.Condition] == 1; % Find positions where the condition = 1
accuracy = [s(idx).Accuracy]; % Find the accuracy values where the condition = 1
number_of_ones = nnz(accuracy) % Count number of ones in 'accuracy'

number_of_ones = 23

or, without the temporary variables:

number_of_ones = nnz([s([s.Condition] == 1).Accuracy])

number_of_ones = 23

[Nienke de Vries]

number_of_ones = nnz([s([s.Condition] == 1).Accuracy])

This worked, thanks so much!! I had already found the nnz function before, but could not figure out how to put the variables between the brackets!

[Austin M. Weber]

@Voss Thank you for the clarification!

[Voss]

@Austin M Weber You're welcome!