Grammar of nounの多さに


> 品揃え **の多さに** ついつい買いこんでしまい、...  
>  I ended up unintentionally buying ??? complete set...

I'm struggling to understand the part in bold. I know that 多い is 'many', and
that you can convert adjectives to nouns by changing the last い to さ. So I get
多さ = 'manyness' (obviously not a real word) maybe 'multitude' or 'multiple'??

Now I have a 'multiple of complete sets' with a に on the end. I can't make any
further sense of it.

I also wondered if when you add a さ the thing you make is a na-adjective
rather than a noun so I could make an adverb from 多さに but that didn't help
either.

I also notice there's no object marker を.




  * 品揃え ≒ _assortment/lineup_ of goods (Probably you can't use _complete set_ here...)
  * I think _abundance_ is the closest noun to 多さ ≒ 豊富さ. 品揃えの多さ ≒ 品揃えの豊富さ means "the largeness of the selection of goods" or simply "the large selection of goods" in this context.
  * 買い込む doesn't necessarily take an object. 買い込む by itself can mean "to do a lot of shopping".
  * This に is a particle which can sometimes mark a cause/reason. (eg, そのニュースに驚いた, その言葉に嬉しくなった) In this case you can understand it as " _because of_ (the abundance)" or " _due to_ (the abundance)".




  * 品揃え ≒ _assortment/lineup_ of goods (Probably you can't use _complete set_ here...)
  * I think _abundance_ is the closest noun to 多さ ≒ 豊富さ. 品揃えの多さ ≒ 品揃えの豊富さ means "the largeness of the selection of goods" or simply "the large selection of goods" in this context.
  * 買い込む doesn't necessarily take an object. 買い込む by itself can mean "to do a lot of shopping".
  * This に is a particle which can sometimes mark a cause/reason. (eg, そのニュースに驚いた, その言葉に嬉しくなった) In this case you can understand it as " _because of_ (the abundance)" or " _due to_ (the abundance)".

