aggelos, I think what you need is something like the datenum function, and not eval. As Per points out, eval'ing a date string is going to treat dashes as subtraction. You might create a new variable in your array,
ds.DateNum = datenum(ds.Date)
if you wanted to keep that around permanently, and then do something like
cal_beg_date = datenum('01-01-2010');
cal_end_date = datenum('31-12-2010');
calData = ds(cal_beg_date <= ds.DateNum & ds.DateNum <= cal_end_date,:)
Don't know what you're doing specifically, so the above may not be exactly what you want, but it should help.
