Reading numeric data from CSV file Matlab for specific columns?

Question

I have two .csv files which I am trying to read into Matlab as numeric matrices. Call it list_a, simply has two columns of ID numbers and corresponding values (appr. 50000 lines) with a ',' delimiter. list_b has 6 columns with a ';' delimiter. I am only interested in the first two columns containing containing numbers; the other columns contain text that I don't care about.

I initially tried using the readtable function in Matlab but noticed that these values aren't stored as numeric values, which is a requirement I have. I couldn't figure out how to cast these as integers after reading them either.

For list_a I have used the dlmread function, which I believes reads the file as numeric values.

For list_b I have tried using the dlmread function in which row and column offsets can be specified (https://www.mathworks.com/help/matlab/ref/dlmread.html#d117e329603) - the problem here is however, that the length of the file could change in the future, so I'm not sure what to enter for the row offsets.

I'm also not sure I understand how this function works, considering I tried testing it for the first 1000 rows as follows:

csv_matrix = dlmread(csv_fullpath,';',[1 1 1000 2]);

and subsequently got the following error message - even though "field number 3" shouldn't even be included in the first place:

Error using dlmread (line 147)
Mismatch between file and format character vector.
Trouble reading 'Numeric' field from file (row number 1, field number 3) ==>
RandomTextInFile\n Error in Damage_List_Reader (line 15)
csv_matrix = dlmread(csv_fullpath,';',[1 1 1000 3]);

I get the impression that I'm making this problem a lot harder than it needs to be so if there's an all around better way to do this, I'm all ears.. Thanks!

Brosch Brosch · Accepted Answer · 2019-11-15T13:36:22

I would suggest using fopen in combination with textscan (e.g. for list_a) like this:

file = fopen('list_a.csv');
out = textscan(file, '%d%f', 'delimiter', ',');
ID = out{1};
Vals = out{2};

'%d%f' specifies the FormatSpec, so the way how the data is formatted in file. With this, you can capture any data from a csv file (and also omit data). I recommend reading the textscan Matlab doc for further formatting issues.

P.S.: I think you can put and "end" (without the quotations) instead of one of the row offset values if the number of rows/cols isn't fixed.

Reading numeric data from CSV file Matlab for specific columns?

1 Answers