I've just noticed the remark
" 5. x e. y is equivalent to (#y) = y i. x."
in the page https://code.jsoftware.com/wiki/Vocabulary/edot#dyadic
However, to spell out the obvious for old hands,
x =. 3 7 13
y =. i.10
x e. y
1 1 0
(#y) = y i. x
0 0 1
(#y) > y i. x
1 1 0
(#y) ~: y i. x
1 1 0
Not so obvious or helpful for "newbies" !
(FWIW, I was exploring how to efficently establish whether elements of
sorted x belong
to sorted y, and if so, their (sorted) indices, for integer vectors x
and y. I'm currently using
e.&y followed by y.&i. on the relatively small list of members of y).
Cheers,
Mike
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