Problems getting the size of a cell array

Question

Anshuman Pal 2020-4-14

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评论： Anshuman Pal 2020-4-14

Hi,

I know that one can usually get the size of a cell array using size(). However, I am facing this particular case -- where I am trying to read data from a .txt file, and save it to a matrix -- where a particular row of the cell (data.textdata{2}) just refuses to show its actual size on using size(). I need the length to loop over data.textdata{2}.

filename = 'test'
data = importdata([filename '.rpt']) ;
%% data is in data.textdata. In particular, data.textdata{2}, which is a matrix, refuses to show its size.
size(data.textdata{2})  % only gives the size of the first character array

I am attaching the code and the text file. Can someone please help?

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Anshuman Pal 2020-4-14

Sorry, the .rpt above and in the code should be substitued with .txt.

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Answer 1

Walter Roberson 2020-4-14

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在 MATLAB Online 中打开

You have

data.textdata{2,1} = [];

That does not delete an existing data.textdata{2,1} : it assigns the empty array inside it.

size(data.textdata{2})

{2} is linear indexing into the 7 x 17478 cell array, and is equivalent to {2,1} when there is more than one row. So size(data.textdata{2}) is the same as size(data.textdata{2,1}) which is the object you just set to [], so the returned size is, quite correctly, 0 x 0.

If you want to know how many entries are in the row, then size(data.textdata,2) --- where 2 refers to the second dimension, not to row number 2.

I would suggest to you that you instead use

data = table2array(readtable([filename '.rpt'], 'headerlines', 4));

and if you have r2019b or later,

data = readmatrix([filename '.rpt'], 'headerlines', 4);