# How to concatenate matrices when some of them can be empty?

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Leon il 15 Dic 2021
Commentato: Leon il 15 Dic 2021
I have 10 matrices, each of them would either have a size of n by 12, or is empty. For example: T1 can be a matrix with a size of 100 x 12, but it can also be []. The same thing goes true for T2, ... T10.
What is the best way to put them together like the below?
vertcat(T1, T2, T3, ... T10)
Many thanks!
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### Risposta accettata

Image Analyst il 15 Dic 2021
I'd do it almost like you. This works fine and has 9 rows because T7 is empty.
T1 = rand(1, 12);
T2 = rand(1, 12);
T3 = rand(1, 12);
T4 = rand(1, 12);
T5 = rand(1, 12);
T6 = rand(1, 12);
T7 = [];
T8 = rand(1, 12);
T9 = rand(1, 12);
T10 = rand(1, 12);
tallerMatrix = vertcat(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10)
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### Più risposte (1)

Voss il 15 Dic 2021
make the empty matrices 0-by-12, then you can vertcat them like normal.
if isempty(T2)
T2 = zeros(0,12);
end
% and so on
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Edric Ellis il 15 Dic 2021
zeros(0,12) generates an empty matrix with the right number of columns. When you vertcat this, it disappears. Like this:
T1 = rand(1, 4);
T2 = zeros(0, 4);
T3 = 10 + rand(1, 4);
vertcat(T1, T2, T3)
ans = 2×4
0.0375 0.3622 0.0174 0.9187 10.5569 10.8928 10.4045 10.8303
Making the right number of columns is not strictly necessary in this case, since vertcat knows how to ignore [] which is of size [0 0].
Leon il 15 Dic 2021
Many thanks!
Interesting to hear the behavior of zeros when vertcating.

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