Writing to file with loops and loop error

Hello, Here is my current code:

clc;
clear;

clear segarray;
block_size = 10000;

filename = 'brktorque-vel-navgraph.txt';
FormatString = ['%*s %s %s %s %s %s %s'];

fid = fopen(filename);
cellchunk = textscan(fid,FormatString,1,'delimiter','\t');

while ~feof(fid)
    tic
   segarray = textscan(fid, FormatString, block_size, 'delimiter',char(9));   
   for i = 1 : 6(segarray);
    segarray{i} = str2double(segarray{i}) ;  
    isn = isnan(segarray{i}) ;
    segarray{i}(isn) = 0 ;
   end
   toc
   [b, ~, n] = unique(segarray(:,6) , 'stable');
    firstColumn  = accumarray(n , segarray(:,4) , size(b) , @(x) min(x));
    secondColumn = accumarray(n , segarray(:,5) , size(b) , @(x) max(x));
    thirdColumn = accumarray(n , segarray(:,3) , size(b) , @(x) mode(x));
    outputArray  = cat(2 , firstColumn , secondColumn , thirdColumn, b);
    csvwrite('brktorque-vel-navgraph-agg.csv',outputArray)
end

fclose(fid);

I have two questions, hopefully you all can provide some assistance: 1. I'm having trouble in the second iteration of my loop with the unique function. The error is "Error using cell/unique (line 86) Input A must be a cell array of strings." I'm not sure why this is happening. 2. I'm worried that my loop will overwrite what is being written to the file in each iteration. I actually want the output of each iteration to be saved after the previous output and all in one file. Am I doing this correctly?

Any help would be greatly appreciated. Thanks in advance!

[Jan]

What does this mean:

   for i = 1 : 6(segarray);

This is no valid Matlab syntax and inconsequence the code should not run at all.

[Muneer]

Hello Jan,

I pull in 6 columns from my file and use that for loop to go through each of the 6 columns and replace null vals, etc. Is there a better way to go about this? Thanks.

Answer 1

[per isakson]

1. Probably segarray(:,6) is empty

    >> unique({[]})
    Error using cell/unique (line 86)
    Input A must be a cell array of strings.

2. csvwrite has no option to append to file. You need to use a function with an append-option, e.g. fopen together with fprintf

Why the while loop?

.

See: I need to learn the Debugger - is there a good tutorial on the net

[Muneer]

The while loop is to pull in 10000 rows at a time until I get to the end of the file. Can this be done in a faster way?

I will try fopen. Thanks for your help!

[per isakson]

You have not described the goal and your constraints well enough.

• How large is the text file?
• How much physical memory (ram) is it in the computer?
• Is speed a real problem?
• Is the format of the file known? What is the purpose of cellchunk

"[...] in a faster way?" Yes, most likely.

• Use the largest possible value of blocksize that memory allows
• Read and convert to numerical in one step with textscan