Is there a way to read only two columns of a file with textscan?

%Get events from text file
prompt_totalfiles = 'Enter number of files you want to input: '; %asks for number of files
total_files = input(prompt_totalfiles);
fileids = cell(total_files,1);

j = 1;
Baseline_adjustment = 0.1; %put in baseline photodetector value here (the readout with the led on but the patch cable in pitch black
wholedff = cell(1, 11);

for file = 1:total_files
[inputfile,path] = uigetfile('*.txt');
fileids{file} = fopen(fullfile(path, inputfile));
if fileids{file} == -1
    error('Failed to open file "%s"', fullfile(path, inputfile));
end

b = textscan(fileids{file},'%n %n',-1, 'delimiter', '/t');
events = b{1};
event_times = b{2};

I am trying to use this code to read in only the first two columns of the text file. However, it doesn't seem to work: what I obtain is a 1x2 cell with [3;1] in the first column and [819;0] in the second one.

Instead, it should be [3; 3; 2; 1; 4; 5; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] and [819; 826; 2279; 3427; 3907; 3919; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0].

Thanks!

Answer 1

[Star Strider]

There are 7 columns in the file image you posted. You can ignore a specific column by putting a * between the % and the descriptor.

Try it with this example (to read only the first 2 columns):

b = textscan(fileids{file},'%n %n %*n %*n %*n %*n %*n',-1, 'delimiter', '/t');

This will not fill the unread columns with 0, it will simply ignore them.

I do not have your file to test this with, so you may need to experiment to get it to do what you want.

See formatSpec for a full discussion.

[Samuele Bolotta]

Thanks! It partially works. I now have a 2x1 cell with 3 in one column and 819 in another. So it seems like it's reading in only the first row.

[Star Strider]

Without your file, it is difficult to accurately underst and what the problem is.

See if adding the 'EndOfLine' name-value pair helps:

b = textscan(fileids{file},'%n %n %*n %*n %*n %*n %*n', 'delimiter', '/t', 'EndOfLine','\r\n');

If problems remain, attach a representative file for me to experiment with.

Also, I do not understand what the ‘-1’ is for. ccording to Specify Repeated Conversion Specifiers and Collect Numeric Data, a number denoting repeats of a format specifier must be a positive integer. Perhaps it is causing problems. (I deleted it in this example.)

According to the documentation, the tab character is '\t', not '/t', however if '/t' gives the result you want, it is likely best not to change it.

Also, another way to skip the remaining fields is described in Skip the Remainder of a Line. I do not usually use that option (I usually want to ignore only specific fields), so I forgot to include it.

[Samuele Bolotta]

As for the -1, I honestly have no idea since my job is precisely to try and make more efficient all of this stuff that was written by a previous person at the lab - whom I don't know. Anyway, I've tried: a) with b) without the -1 c) changing the '/t': I still got the same output: a 3 and a 819.

But by doing this:

b = textscan(fileids{file},'%n %n %*[^\n]', -1, 'delimiter', '\t', 'EndOfLine','\r\n');

I solved the issue and it now works!

This gives me the same correct results:

b = textscan(fileids{file},'%n %n %*[^\n]', 'delimiter', '/t');

So adding

"%*[^\n]" 

is what really made the difference, even tho I'm not sure why what you originally proposed affects reading in the other rows. I attached the file anyway. Thanks!

[Star Strider]

As always, my pleasure!

Answer 2

[darova]

Read whole data using importdata or readtable and choose only columns you want