Importing data from a file in a specific way

Question

g 2019-3-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/450614-importing-data-from-a-file-in-a-specific-way

回答： Walter Roberson 2019-3-17

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

I have a file with 3 columns of data.

Here is just a sample of what the data looks like (there are many more rows):

54555556 1.09773e-46 1.04772e-23
54611111 3.60808e-47 6.00673e-24
54666667 1.25291e-46 1.11934e-23

I want to read this into Matlab (with the numbers formatted with the same precision) and be able to work with specific columns. This is what I have. I'm not sure what is going wrong or if I even am reading in the numbers properly for their values.

fileID = fopen(file,'r');
formatSpec='%f %12.5e %12.5e';
sizeA = [Inf 3];
A = fscan(fileID,formatSpec,sizeA);
disp(A);

Additionally, once I have this working, how would I select a specific column?

Thanks!

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g 2019-3-17

编辑：g 2019-3-17

There is no specific reason, I suppose. I was just trying to avoid those very small numbers being interpreted as 0.0000 for instance- I want them to keep their values on the order of 10^-46, etc. I don't believe I'm working with fixed width.

Walter Roberson 2019-3-17

%f knows about exponential format.

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Answer 1

Walter Roberson 2019-3-17

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fileID = fopen(file, 'r');
formatSPec = '%f %f %f';
sizeA = [3 Inf];   %notice not [Inf 3]
A = fscanf(fileID, formatSpec, sizeA) .';   %notice transpose
fclose(fileID);

Or

A = cell2mat( textscan( fileread(file), '%f %f %f') );

And afterwards, A(:,2) would be the second column.

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Answer 2

Guillaume 2019-3-17

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The numbers in your text file have less precision than matlab uses. So, the simplest thing is to load them with csvread (or dlmread):

data = csvread(file);

Note that the precision with which matlab displays the numbers is completely different to the precision at which they're stored. Use format to change the display precision.