# Why is this generating a numerical array and not an array of cells?

1 view (last 30 days)
Nicholas Kavouris on 17 Mar 2022
Commented: Image Analyst on 17 Mar 2022
Why does the following loop generate slope as the result of diff() function? Instead or a cell array with the desired text?
for i=1:length(Temp_F)
if diff(Temp_F(i))>0
slope(i)='Rising'
elseif diff(Temp_F(i))<0
slope(i)='Falling'
end
end
Stephen23 on 17 Mar 2022
diff(Temp_F(i))
What do you expect the difference of one number to be?

KSSV on 17 Mar 2022
REad about the function diff. It needs an array with atleast 1x2 dimensions. You are giving only one number as input. So diff gives you an empty matrix.
diff(1)
ans = []
diff(rand)
ans = []
diff(rand(1,2))
ans = 0.0347
diff(rand(2,1))
ans = 0.5240
So you have to modify your code like below:
diff_Temp_F = diff(Temp_F) ; % I assume Temp_F is a vector
N = length(Tmp_F) ;
slope = cell(N,1) ;
for i=1:length(Temp_F)-1
if diff_Temp_F(i) > 0
slope{i}='Rising'
elseif diff_Temp_F(i) < 0
slope{i}='Falling'
end
end
Image Analyst on 17 Mar 2022
I believe you could also use strings instead of character arrays and then use parentheses instead of braces
slope(i) = "Rising"; % Use double quotes instead of single quotes.

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