how to sort a matrix based on a specific value and bring the row at the beginning of the file

Hi all, i want to do a strange sort into my file. I have a file which contains values like:

100 200 x1

201 340 x2

341 400 x4

405 460 x1

461 500 x5

501 600 x1

etc

I want in a way to search for the rows that in their 3rd column have the value x1 and then put the whole row at the beginning of the file. So as an output i d like to have something like:

100 200 x1

405 460 x1

501 600 x1

201 340 x2

341 400 x4

461 500 x5

any ideas? thanks in advance.

Answer 1

[Image Analyst]

See if you can put a row at the beginning that's column names, like

c1, c2, c3

Is that a possibility? If so, it makes it easier since you can use readtable().

Then try readtable() to read it in

t=readtable(filename);

Then sort the third column. Extract the third column like

column3 = t.c3;

then see if you can use sort(). Take both outputs of sort. Use the sort order to sort the rows of the other columns. Is this homework? If not, attach your data file.

[Daniel Barzegar]

Here is the attached file.

[Daniel Barzegar]

Columnds 1 and 2 represent the start and end time of an instance respectively, whereas the 3rd column is the label. So, for example for the label 4 i want to bring all the start-end time rows at the beginning of the file.

i hope it's more clear now what i want to do.

[Image Analyst]

OK, so column 3 actually is not "x1" or "x2" or any other strings, but it's actually a floating point number. In that case you can just use dlmread() and sortrows() (as Roger actually suggested before me):

filename = 'damyannotation.txt';
M = dlmread(filename)
sortedM = sortrows(M, 3)

Answer 2

[Roger Stafford]

If you put that data in a single matrix M, the 'sortrows' function will do what you want:

   M = sortrows(M,3);