.Q.gz[::]           / zlib loaded?
.Q.gz cbv           / unzipped
.Q.gz (cl;cbv)      / zipped

Where

• cbv is a char or byte vector
• cl is compression level [1-9] as a long

returns, for

• the general null, a boolean atom as whether Zlib is loaded
• cbv, the inflated (unzipped) vector
• a 2-list, the deflated (zipped) vector

since V4.0 2020.04.16.

q).Q.gz{0N!count x;x}[.Q.gz(9;10000#"helloworld")]
66
"helloworldhelloworldhelloworldhelloworldhelloworldhelloworldhelloworldhellow..