How to extract data from data file?

Hi

I've a .txt file with over 50000 lines(exact number of lines unknown) with 20 parameters(in line 1, the rest of the lines are data). I need to get two different parameters(column number 2 and number 12) from it. How can I do this the smartest way?

Answer 1

[dpb]

By current memory, that's not all that big any longer...probably just as easy to just load the file and then trash the columns don't need/want...

Many possible choices...

x=importdata('yourfile.txt','headerlines',1);   % read the file
x=x(:,[2 12]);                                  % keep only the columns wanted

Alternatively, only read the two columns...

fmt=['%*f %f' repmat('%*f',1,9) '%f' repmat('%*f',1,8]);  % a format string
x=textread('yourfile.txt',fmt,'headerlines',1);           % read 'em in...

Many variations of the above are possible...see

help iofun

for list of all the i/o functions; choose from one of the above or from the list the one that strikes your fancy for the file format...

[hmtrondheim Tróndhiem]

When I use the first method I get an error message saying: Index exceeds matrix dimensions. What can I do about that?

[dpb]

Make sure importdata works to begin with.

Show your exact code and result of

whos x

afterwards as well as

exist('yourfile.txt','file')

Wouldn't hurt to paste a short section of the file just to make sure we know what we're talking about...