You can write using a block or write the code on one line when nesting maps. This code shows you how to do both.

block_or_line.rb

#Code with block
$myvariable= imgarray.map do |layouts|
  layouts[ 'layouts' ].map do |layout_name|
    layout_name['layout_name']
  end
end


#Code on one line
$myvariable= (imgarray.map{ |layouts| (layouts[ 'layouts' ]).map{ |layout_name| (layout_name[ 'layout_name' ]) }} )