Is there any relative pronoun omitted?

I came across the sentence as follows, and I cannot make out its structure.

[ That was some quick thinking you did. ]

The situation is like this.  "I" did a marvelous thing to help "you"  in danger.

And "you" thanked me and said as above.

What's the relation between the clauses, That was some quick thinking and

you did ?  

I thank you in advance.

Kayoh wrote:

I came across the sentence as follows, and I cannot make out its structure. [ That was some quick thinking you did. ] The situation is like this.  "I" did a marvelous thing to help "you"  in danger. And "you" thanked me and said as above. What's the relation between the clauses, That was some quick thinking and you did ?   I thank you in advance.

That was some quick thinking (which or that) you did.

That was some quick thinking is the principal clause, while that or which you did is a relative adjectival clause. The latter modifies and limits the former.

Kayoh wrote:

I came across the sentence as follows, and I cannot make out its structure. [ That was some quick thinking you did. ] The situation is like this.  "I" did a marvelous thing to help "you"  in danger. And "you" thanked me and said as above. What's the relation between the clauses, That was some quick thinking and you did ?   I thank you in advance.

That was some quick thinking you did.

The noun clause, the object of did,  is fronted.

You did some quick thinking -- fronting for emphasis --  Some quick thinking you did -- object in pre-verbal subject territory -- heal the problem -- proform with cataphoric reference --  That was ... -- okay