# How to use cellfun?

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Tomaszzz on 22 Mar 2022
Commented: Voss on 22 Mar 2022
Hi all,
I have two 21 x1 cells (t_sq_mtw / t_sq_dot_1) containg 100x18 tables.
The below code calculates three parameters (a0_longhand/ a1_longhand/rSq_longahnd) for one variable (P_acc_z_meancycle) from correspoding first pair of tables.
I was wondering how could I apply cellfun to apply the code to all tables (not just one as in the code below)? Can you help please?
Pref = (t_sq_mtw{1, 1}.P_acc_z_meancycle); %variable one from data set 1
Pa = (t_sq_dot_1{1, 1}.P_acc_z_meancycle); %%variable one from data set 2
for i=1:length(Pref)
temp_toprow(i)=(Pref(i,1)-mean(Pref))*(Pa(i,1)-mean(Pa));
temp_bottomrow(i)=(Pref(i,1)-mean(Pref))^2;
end
toprow=sum(temp_toprow);
bottomrow=sum(temp_bottomrow);
a1_longhand=toprow/bottomrow;
a0_longhand=mean(Pa)-(a1_longhand*mean(Pref));
n=length(Pa);
x=Pref;
y=Pa;
toprow=(n*(sum(y.*x)))-(sum(x)*sum(y));
bottomrow=sqrt(((n*sum(x.^2))-(sum(x))^2)*((n*sum(y.^2))-(sum(y))^2));
r=toprow/bottomrow;
rSq_longhand=r^2;
if a1~=a1_longhand
warning(1)=1;
else
warning(1)=0;
end
if a0~=a0_longhand
warning(2)=1;
else
warning(2)=0;
end
if rSq~=rSq_longhand
warning(3)=1;
else
warning(3)=0;
end
This is the first part of the code were cellfun is sucessfully used.
% do polyfit() of P_acc_z_meancycle for each pair of tables
p = cellfun(@(x,y)polyfit(x.P_acc_z_meancycle,y.P_acc_z_meancycle,1), ...
t_sq_mtw,t_sq_dot_1,'UniformOutput',false);
p = cell2mat(p); % p is a 21-by-2 matrix of coefficients from polyfit()
a1 = p(:,1);
a0 = p(:,2);
% do corrcoef() of P_acc_z_meancycle for each pair of tables:
r = cellfun(@(x,y)corrcoef(x.P_acc_z_meancycle,y.P_acc_z_meancycle), ...
t_sq_mtw,t_sq_dot_1,'UniformOutput',false);
rSq = cellfun(@(x)x(1,2)^2,r); % rSq is a 21-by-1 column vector of r-squared values from corrcoef()

Voss on 22 Mar 2022
You can make that code into its own function and then use cellfun() to call that function on all pairs of tables:
% call get_longhand() on each pair of tables' P_acc_z_meancycle
[a1_longhand,a0_longhand,rSq_longhand] = cellfun( ...
@(x,y)get_longhand(x.P_acc_z_meancycle,y.P_acc_z_meancycle), ...
t_sq_mtw,t_sq_dot_1);
disp([a1_longhand a0_longhand rSq_longhand]);
0.9867 0.1336 0.9849 1.0177 0.1576 0.9866 0.9638 0.1300 0.8919 -0.4362 0.0891 0.3034 0.7685 0.1178 0.8005 0.5379 0.1677 0.2836 1.0999 0.1258 0.9708 0.9652 0.1466 0.8687 0.9787 0.2405 0.9272 1.2832 0.4761 0.6527 0.9320 0.1208 0.9839 0.9377 0.0799 0.8746 0.9965 0.1056 0.9026 0.0039 0.1945 0.0000 1.0158 0.1026 0.9746 1.0483 0.1801 0.9568 1.2828 0.2525 0.4985 0.9924 0.1191 0.9674 0.9760 0.1164 0.9577 0.5547 0.0885 0.3260 1.0794 0.2551 0.7127
function [a1_longhand,a0_longhand,rSq_longhand] = get_longhand(Pref,Pa)
for i=1:length(Pref)
temp_toprow(i)=(Pref(i,1)-mean(Pref))*(Pa(i,1)-mean(Pa));
temp_bottomrow(i)=(Pref(i,1)-mean(Pref))^2;
end
toprow=sum(temp_toprow);
bottomrow=sum(temp_bottomrow);
a1_longhand=toprow/bottomrow;
a0_longhand=mean(Pa)-(a1_longhand*mean(Pref));
n=length(Pa);
x=Pref;
y=Pa;
toprow=(n*(sum(y.*x)))-(sum(x)*sum(y));
bottomrow=sqrt(((n*sum(x.^2))-(sum(x))^2)*((n*sum(y.^2))-(sum(y))^2));
r=toprow/bottomrow;
rSq_longhand=r^2;
end
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Voss on 22 Mar 2022
You're welcome!