Method: Arrow::ColumnContainable#select_columns

Defined in:
lib/arrow/column-containable.rb

#select_columns(*selectors) {|column| ... } ⇒ self.class

Selects columns that are selected by selectors and/or block and creates a new container only with the selected columns.

Parameters:

  • selectors (Array<String, Symbol, Integer, Range>) —

    If a selector is String, Symbol or Integer, the selector selects a column by #find_column.

    If a selector is Range, the selector selects columns by ‘::Array#[]`.

Yields:

  • (column) —

    Gives a column to the block to select columns. This uses ‘::Array#select`.

Yield Parameters:

  • column (Column) —

    A target column.

Yield Returns:

  • (Boolean) —

    Whether the given column is selected or not.

Returns:

  • (self.class) —

    The newly created container that only has selected columns.



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# File 'lib/arrow/column-containable.rb', line 74

def select_columns(*selectors, &block)
  if selectors.empty?
    return to_enum(__method__) unless block_given?
    selected_columns = columns.select(&block)
  else
    selected_columns = []
    selectors.each do |selector|
      case selector
      when Range
        selected_columns.concat(columns[selector])
      else
        column = find_column(selector)
        if column.nil?
          case selector
          when String, Symbol
            message = "unknown column: #{selector.inspect}: #{inspect}"
            raise KeyError.new(message)
          else
            message = "out of index (0..#{n_columns - 1}): "
            message << "#{selector.inspect}: #{inspect}"
            raise IndexError.new(message)
          end
        end
        selected_columns << column
      end
    end
    selected_columns = selected_columns.select(&block) if block_given?
  end
  self.class.new(selected_columns)
end