I'm trying to run a linear regression on cases that fit certain criteria, can you help?

I have a matrix I downloaded from excel:

clear all 
x = xlsread('excelspreadsheet.xlsx');
z = xlsread('BR5_BR4.xlsx', 'A:A');

x = 
1.35   0.006051407  -0.001325416  -0.000295  -6.20E-05
 1.13   -0.002442044  -7.60E-06  -4.50E-05  3.40E-05
 1.04   0.005803107  -0.000637415  0.000394  0.000723
 1.01   0.005687193  -0.000856177  0.000141  0.000628
 0.86   -0.003891923  -0.000814317  0.001307  0.001105
 0.82   -0.001361756  -0.000658948  -0.001778  -0.001301
 0.73   -0.002613974  -0.000814317  0.001307  0.001383
 0.68   -0.003173712  0.000683247  1.40E-05  0.000796
 0.60   0.00154659  -0.000254445  2.80E-05  0.00033

I want go through the matrix and select rows where certain columns have values > or < 0. Then I want to run a regression on the rows that meet these terms. This is what I came up with, but it isn't working. Can anyone help?

if x( x(:,2)>0 & x(:,3)<0 & x(:,4)<0 & x(:,5)<0 , :) 
    md1 = lm(x, z);

end

Answer 1

[Brendan Hamm]

The if statement must have a scalar logical statement next to it (either true or false) but what you have is a numeric matrix.

If what you are trying to do is extract only rows where x(:,2) > 0 and x(:,3) < 0 and x(:,4) < 0 and x(:,5) < 0 for the regression, but it may be the case that this does not have any data, I would suggest.

rows = x(:,2)>0 & x(:,3)<0 & x(:,4)<0 & x(:,5)<0; % Logical vector with the rows which satisfy all conditions.
if any(rows) % True if there is at least 1 row which meats the condition.
    mdl = fitlm(x(rows,:),z(rows)); % Fit with the rows which satisfy condition.
end

Really you wouldn't want only one row to satisfy the condition as you would require that x(rows,:) is an invertible matrix.