Can we using regular expression in xpath value?
You could have theoretically used matches(), but it is a part of xpath 2.0, which webdriver doesn't support, see a detailed explanation here:
Apply a starts-with() check instead:
//*[starts-with(@id, "ngdialog")]
Using XPath 2.0 :
:xpath,'//*[matches(@id, '^(ngdialog)[0-9]')]/div[2]/div[2]/table/tbody/tr/td[1]/input'
Since you are using Watir, you could also use a regular expression to find the ngdialog element. XPath could then be used for the other portion of the path (note the starting of the XPath with ./ is used to tell Watir to look within the ngdialog):
browser.element(:id => /ngdialog/).checkbox(:xpath => './div[2]/div[2]/table/tbody/tr/td[1]/input')