May I please know how the over iterator is being used here?

[kdb_newbie]

Which form of iterator is being used here? Thank you! 

https://code.kx.com/q4m3/A_Built-in_Functions/#a88-ssr 

You can use the over iterator with ssr to replace multiple items.

(ssr/)["results_%div_%dept.csv"; ("%div";"%dept"); ("banking";"m&a")]

[rocuinneagain · Accepted solution]

https://code.kx.com/q/ref/accumulators/#ternary-values

You can use a sample to see how it progresses:

({-1 .Q.s1 `x`y`z!(x;y;z);x+y+z}/)[0;1 2 3;4 5 6]
`x`y`z!0 1 4
`x`y`z!5 2 5
`x`y`z!12 3 6
21

And on the ssr example:

({-1 .Q.s1 `x`y`z!(x;y;z);ssr[x;y;z]}/)["results_%div_%dept.csv"; ("%div";"%dept"); ("banking";"m&a")]
`x`y`z!("results_%div_%dept.csv";"%div";"banking")
`x`y`z!("results_banking_%dept.csv";"%dept";"m&a")
"results_banking_m&a.csv"

[kdb_newbie]

Thank you very much! May I ask where is the documentation on "-1" used here? 

[eohara_kdb]

Handles to files and processes | Basics | q and kdb+ documentation - Kdb+ and q documentation (kx.co...

1 means send to stdout

-1 means send to stdout, then append a newline character