APL (Dyalog Extended), 16 12 bytes
Anonymous tacit prefix function, port of Bubbler's J.
⊢⊂⍨1=1⊥2⊤⍳∘��
⊢ the argument…
⊂⍨ partitioned by…
1= where one equals…
1⊥ the vertical sum (lit. base-1 evaluation) of…
2⊤ the binary representation (one number per column) of
⍳∘ the indices from 1 to the…
≢ length of the argument
Alternative APL (Dyalog Unicode), 12 bytes
Anonymous tacit prefix function, port of noodle person's J.
⊢⊆⍨1+∘⌊2⍟⍳∘≢
⊢ the argument…
⊂⍨ grouped by…
1+∘ incremented…
⌊ floored…
2⍟ log₂ of…
⍳∘ the indices of…
≢ the argument length
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Old APL (Dyalog Unicode), 16 bytes
Anonymous tacit prefix function. Requires 0-based indexing (⎕IO←0) which is default on many systems.
⊢⊂⍨≢↑∘∊1↑¨⍨2*⍳∘≢
⊢ the argument…
⊂⍨ partitioned by…
≢ the length of the argument…
↑∘∊ -sized prefix of the the flattened…
1↑¨⍨ prefixes of 1 (padding with trailing 0s) of lengths…
2* two to the power of…
⍳∘≢ the indices (0…n−1) of the length of the argument