xpath - Rspec capybara check if substring is in string result -

ok trying rspec capybara test table resultset.

so have table

**username   fullname   address  location**     simon      simon lau   ny          foo.bar    foo bar     au        au 

now want first row , check if username (simon) contains string(mon)

how can dynamically using rspec capybara if take consideration values might change want check first row , username column.