Here are a few examples with Spreadsheet gem

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#Defining formats   float_format   = Spreadsheet::Format.new :number_format => "#,##0" percent_format = Spreadsheet::Format.new :number_format => "0.00%" bold_format    = Spreadsheet::Format.new :weight => :bold cell_format    = Spreadsheet::Format.new :bottom => :medium,                                          :horizontal_align => :center,                                          :weight => :bold   #Implementation   sheet.default_format = float_format.                    #Format sheet sheet.column(col_idx).default_format = percent_format   #Format a column sheet.row(row_idx).default_format = bold_format         #Format a row sheet.row(row_idx).set_format(col_idx, cell_format)     #Format a cell   sheet.column(1).width = 12                              #Format column width