How to conditionally import data from a spreadsheet into MATLAB without using a loop

Question

Given a spreadsheet with variables in columns and observations in rows, I would like to selectively import those observations into MATLAB whose value in a specified column is equal to a specified string (in this case 'K' ). I am aware of the possibility to use a loop but my data set is very large and I would prefer a faster solution (logical indexing?). I am using a table variable.

I would greatly appreciate any suggestions. I have found multiple solutions online to do this for array variables, but not for table variables.

My spreadsheet looks like this:

Variable1    Variable2    Variable3
234789       234678234    'K'
98764        087632167    'V'
87641        492876437    'V'
43789234     123678923    'K'

In this example I would only want to import rows 1 and 4 (not counting headers) because they have value 'K' for Variable3 .

I have tried tableName(tableName(:,3) ~= 'K', :) = [] after importing the entire dataset but I get an Undefined operator '~=' for input arguments of type 'table' error message.

Answer 1

Ok there is probably a better answer but here is what I know. I've never been able to use this kind of logic:

tableName(tableName(:,3) ~= 'K', :) = []

Even if you were using the correct kind of logical comparison between something in a table and a character (table ~= 'K') you will probably have issues with the way you are trying to use the logic.

To do what you want without looping, I typically create a temporary variable that contains only the column of the variable that will determine which rows to keep. Here's an example of what I mean...

data = {1,2,'b';3,4,'c';5,6,'d';7,8,'d'};

%find which rows where the third column is 'd'
temp = data(:,3);%create temporary variable
out = strcmp(temp,'d');%returns logical 1 where strings are the same
index = find(out);%returns the indexes of which rows contain 'd'

data = data(index,:);%now you only have the rows containing 'd'