row by row matrix building

2015 11 6
1 个回答
更新时间：2015 11 9
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0 个投票

Quick question here I hope. Am modifying some code, can't see why this won't work:
j=1
while ischar (tline);
%define indexes, below as idx, etc etc
tline = fgetl(fid); %reads the next line in input file
dt = textscan(tline,'%s','delimiter',',');
tm = datenum(dt{1}(didx));
d1 = str2double(dt{1}(1idx));
d2 = str2double(dt{1}(2idx));
d3 = str2double(dt{1}(3idx));
mat(j,:) = [tm d1 d2 d3]; ;
j = j+1;
tline = fgetl(fid);
end;
The stumbling block is the mat(j,:) portion. Error message says 'Subscripted assignment dimension mismatch.' Tried different ways of creating mat[] prior to this loop and in different ways but no luck. Could do a whole different approach, but don't want to build a whole new routine.

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回答（1 个）

Image Analyst
Image Analyst 2015-11-7

0 个投票

What is the size of mat? Does it have 4 columns? What is the value of tline and j when the error is thrown? Maybe try preallocating mat before the while loop
mat = zeros(1, 4);

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Colin Edgar
Colin Edgar 2015-11-7
The example data being tested is 40449 x 7, actual size varies. So 7 columns (posted code has 4). When error is thrown, j = 1 and tline is the first line of data. I tried preallocating mat in different ways mat[], mat = zeros(x,y) etc. Is the indexing approach correct:
mat(j,:) = [tm d1 d2 d3 etc]; ?
Image Analyst
Image Analyst 2015-11-7
Yes, as long as there are the same number of elements on the right hand side as there are columns in the matrix. Can you finish answering my questions, like what is tline?
Colin Edgar
Colin Edgar 2015-11-7
Here's the rest of the code:
flnm = 'C:\testfile.csv'
fid = fopen(flnm);
j = 1;
tline = fgetl(fid); %reads past top header lines
tline = fgetl(fid); %reads past top header lines
mat = zeros(40449,7);
while ischar(tline)
.....then what I posted initially
tline='2015-05-16 12:54:00,65433,0,1,402.2262,3.598117,99.87829,-5.04303,1.07'
It will sometimes go through j = 1 and then first row of mat is populated correctly. Then it bombs on j = 2. error**Improper assignment with rectangular empty matrix.
Image Analyst
Image Analyst 2015-11-7
Well you can't assign 4 numbers to an entire row of 7 columns. If you just want the first 4 columns assigned, you can index it like this:
mat(j,1:4) = [tm d1 d2 d3];
The final 3 columns (columns 5, 6, and 7) will be untouched and remain as zero.
Colin Edgar
Colin Edgar 2015-11-9
I realize that. Sorry my example is smaller than my actual testfile. I still haven't solved this but am doing a workaround. Still interested in a solution. Thx

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