how do I use importdata() to import specific columns of data from a .txt file?

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Mehrab 2023-9-13

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https://ww2.mathworks.cn/matlabcentral/answers/2020451-how-do-i-use-importdata-to-import-specific-columns-of-data-from-a-txt-file

评论： Walter Roberson 2023-9-14

bubbles.txt

The file is called bubbles.txt and has been attached to this question. I'm trying to import the hours accessed and cumulative bubbles columns, however, I am not completely sure how to proceed. So far my code looks like this:

clear all; close all; clc
M = importdata('bubbles.txt', ' ', 1);
for k = [1, 3]
    disp(M.colheaders(1, k))
    disp(M.data(:, k))
    disp(' ')
end

This returns an error saying:

Dot indexing is not supported for variables of this type.
Error in lab8t2 (line 9)
disp(M.colheaders(1, k))

How can I solve this issue?

Regards

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Stephen23 2023-9-13

" How can I solve this issue?"

Avoid fragile IMPORTDATA. Use READTABLE instead.

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Answer 1

dpb 2023-9-13

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https://ww2.mathworks.cn/matlabcentral/answers/2020451-how-do-i-use-importdata-to-import-specific-columns-of-data-from-a-txt-file#answer_1309281

编辑：dpb 2023-9-13

在 MATLAB Online 中打开

bubbles.txt

importdata returns an array, not a struct nor table -- it has its uses, but I generally avoid it for more specific functions that do what really want. There's no real reason to not just read the file instead of getting too fancy; here a table would seem appropriate--

tBubbles=readtable('bubbles.txt');
Warning: Column headers from the file were modified to make them valid MATLAB identifiers before creating variable names for the table. The original column headers are saved in the VariableDescriptions property.
Set 'VariableNamingRule' to 'preserve' to use the original column headers as table variable names.
head(tBubbles)
    PhotoNumber    HoursElapsed    Bubbles    CumulativeBubbles
    ___________    ____________    _______    _________________

         1               1           117             117       
         2               2            96             213       
         3               4           180             393       
         4               6           128             521       
         5               8           115             636       
         6              10            94             730       
         7              12            94             824       
         8              14            67             891       

and you've got everything...and now dot indexing will return the respective data you want directly...

plot(tBubbles.HoursElapsed,tBubbles.CumulativeBubbles)

xlabel('Hours'), ylabel('Number Bubbles (Total)')

for example...

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Mehrab 2023-9-14

Ahhh I see. Thank you, I appreciate the help makes a lot of sense now!

Walter Roberson 2023-9-14

importdata() can return any of three different datatypes, depending on what data it finds in the file. I recommend against using it, recommending that instead you use a function such as readtable() that returns predictable datatype.

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