# Creating a For Loop to Compare Every Two Cells in Array

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oronir on 5 Oct 2023
Commented: Walter Roberson on 5 Oct 2023
Hi All,
I want to create a loop that compares every two values in an array.
For example:
HD_Affect = ["Neutral" "Positive" "Negative" "Positive" "Neutral" "Negative"]
if "Neutral" then "Positive" || "Negative" then "Positive"
Res = "Positive";
elseif "Neutral" then "Negative" || "Positive" then "Negative"
Res = "Negative";
elseif "Positive" then "Positive" || "Neutral" then "Neutral" || "Negative" then "Negative"
Res = "Same";
else
Res = "NaN";
end
I want to be able to compare 1 and 2, 3 and 4, 5 and 6, and so on.
I would then want each of these results put into the variable Res where I could then use summary(Res) or another way to identify the number of times each of these (Positive, negative, same) happens.
Does anyone know if there is a way to set up a For loop that would compare every 2 elements in the array using the If statements outlined and combine the answers into a separate array? I hope this isn't two confusing and would appreciate any help I could get. Thank you!
Walter Roberson on 5 Oct 2023
Does it need to be a for loop? Because you can simplify the code by using a 2D array, including with using categorical as indices.
%for example after having constructed appropriate categoricals,
Results(Neutral,Positive) = Positive;
Results(Negative,Positive) = Positive;
%and later
Res = Results(FirstInput, SecondInput)

Fabio Freschi on 5 Oct 2023
Edited: Fabio Freschi on 5 Oct 2023
I try to translate your pseudocode into Matlab instructions
HD_Affect = ["Neutral" "Positive" "Negative" "Positive" "Neutral" "Negative"];
% preallocation
Res = strings(1,length(HD_Affect)/2);
% loop
for i = 1:2:length(HD_Affect)
if strcmpi(HD_Affect(i),"Neutral") & strcmpi(HD_Affect(i+1),"Positive") ...
|| strcmpi(HD_Affect(i),"Negative") & strcmpi(HD_Affect(i+1),"Positive")
Res((i+1)/2) = "Positive";
elseif strcmpi(HD_Affect(i),"Neutral") & strcmpi(HD_Affect(i+1),"Negative") ...
|| strcmpi(HD_Affect(i),"Positive") & strcmpi(HD_Affect(i+1),"Negative")
Res((i+1)/2) = "Negative";
elseif strcmpi(HD_Affect(i),"Positive") & strcmpi(HD_Affect(i+1),"Positive") ...
|| strcmpi(HD_Affect(i),"Neutral") & strcmpi(HD_Affect(i+1),"Neutral") ...
|| strcmpi(HD_Affect(i),"Negative") & strcmpi(HD_Affect(i+1),"Negative")
Res((i+1)/2) = "Same";
else
Res((i+1)/2) = "NaN";
end
end
disp(Res)
"Positive" "Positive" "Negative"

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