Extracting table from data structure

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Haresh Kumar
Haresh Kumar 2021-4-6
评论： Haresh Kumar 2021-4-6
Hello,
I have multile .mat files and from these files I want to extract the table with variable name B (500000×1 double). At first, I have loaded data using S = dir('*.mat'); and then I am using commond K = S.B; to extract the data from table variable name B. This commond doesnot work and gave me this message: Reference to non-existent field 'B'.. Can you guide me which commond will I use to extract the table data from data structure.
Br,
Haresh Kumar
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Stephen23
Stephen23 2021-4-6
编辑：Stephen23 2021-4-6
@Haresh Kumar: that certainly looks like the structure returned by DIR, which by default does not contain a "B" field.
Most likely you forgot to actually import some file data (possibly into a table).
Haresh Kumar
Haresh Kumar 2021-4-6
Hello,
Let me make it simple. I am giving directory path inorder to run the multiple .mat files from the folder. Each .mat file (number (1)......number(n)) contains multiple tables from which I only want the table of variable B. Now, you can guide which commond will I use to get the data from variable B (Table)
Br,
Haresh Kumar

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回答（2 个）

Hiro Yoshino
Hiro Yoshino 2021-4-6
First thing you should do is check if S is a table variable.
If it turns out to be a table variable, then the next thing would be running the following command to check if B exists
S.Properties.VariableNames
Good luck.
Steven Lord
Steven Lord 2021-4-6
Ran in:
At first, I have loaded data using S = dir('*.mat');
The dir function does not load data. All it does is generate a list of files in the directory with the .mat extension. To load the data you'll need to use the load function. Then if you want to check if the loaded data contains a variable named B (that has been loaded into a field of the output of load you can use isfield.
data = load('census.mat')
data = struct with fields:
cdate: [21×1 double] pop: [21×1 double]
doesItHaveAVariableB = isfield(data, 'B')
doesItHaveAVariableB = logical
0
doesItHaveAVariableCdate = isfield(data, 'cdate')
doesItHaveAVariableCdate = logical
1

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