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Find where list items change value

differ x    differ[x]

Returns a boolean list indicating where consecutive pairs of items in x differ. It applies to all data types.

It is a uniform function. The first item of the result is always 1b:

    r[i]=1b                 for i=0
    r[i]=not A[i]~A[i-1]    otherwise
q)differ 1 3 3 4 5 6 6

Split a table with multiple dates into a list of tables with distinct dates.

q)d:2009.10.01+asc 100?30
q)i:where differ t[`date]    / indices where dates differ
q)tlist:i _ t                / list of tables with one date per table
q)tlist 0
date       sym  price    size
2009.10.01 IBM  37.95179 710
2009.10.01 CSCO 52.908   594
2009.10.01 MSFT 32.87258 250
2009.10.01 CSCO 75.15704 592
q)tlist 1
date       sym  price   size
2009.10.02 MSFT 18.9035 26
2009.10.02 CSCO 12.7531 760
domain: b g x h i j e f c s p m d z n u v t
range:  b b b b b b b b b b b b b b b b b b
Binary use deprecated

As of V3.6 the keyword is variadic. Binary application is deprecated and may disappear in future versions. The keyword cannot be applied infix.

For a binary version, use Match Each Prior: ~:'.

Basics: Comparison

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