Earlier quoted context omitted.
words←⊃⎕nget 'wordlist.txt' 1 ⍝ read lines tenK←'^........k.$' ⎕S '&' ⊢ words ⍝ regex filter ↑tenK/⍨{∧/1='abc'(+/∘.∊)⍵}¨tenK ⍝ count abc and filter Dyalog APL, but it's still kinda ... heavy.
> tenK←'^........k.$' ⎕S '&' ⊢ words ⍝ regex filter Is tenK←{(10=≢⍵)∧⍵[9]='k'}¨words better? Feel that better matches the problem spec, although requires the each
⍵[9] INDEX ERRORs on the shorter words, and that code needs a compress to do the filtering. It's a more traditional and faster approach, which is better from those viewpoints. If faster and avoiding each and using array concepts is desirable, how about:
words←↑⊃⎕nget 'wordlist.txt' 1
tenK←words⌿⍨('k'=words[;9])∧(' '≠words[;10])∧(' '=words[;11])
tenK⌿⍨{∧/1='abc'(+/∘.∊)⍵}⍤1⊢tenK