step definition to test the contents of specific table row given a column heading and the contents of one of the cells in the row

table cell locator.rb

# Locates a table cell based on given row and column content.
When /^(.*) in the "([^\"]*)" column of the "([^\"]*)" row$/ do |action, column_title, row_title|
  col_number = 0
  all(:xpath, "//*[(th|td)/descendant-or-self::*[contains(text(), '#{column_title}')]]/th").each do |element|
    col_number += 1
    break if element.has_content?(column_title)
  end
  within :xpath, "//*[(th|td)/descendant-or-self::*[contains(text(), '#{row_title}')]]/td[#{col_number}]" do
    When action
  end
end

This is exactly what I have been looking for but I'm a little confused about how to use it. I basically have a table and I know the column title that contains the value I want (to assign to a variable) along with a value within that row. (The row itself doesn't have a title) When I try to run it with cucumber I get an undefined error.

What would the cucumber look like?
When in the "A" column of the "B" row ?