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A local variable named log contains an array of hashes with timestamped events like so log = [ {time: 201201, x: 2}, {time: 201201, y: 7}, {time: 201201, z: 2}, {time: 201202, a: 3}, {time: 201202, b: 4}, {time: 201202, c: 0} ]

Please collapse the log by date into an array of hashes containing one entry per day [ {time: 201201, x: 2, y: 7, z: 2}, {time: 201202, a: 3, b: 4, c: 0}, ]

Ordering in the input is not defined. Ordering in the result is not important. Do not rely on the names of the hash keys other than :time. The field below executes your code in a Sandbox with $SAFE=4, so you can't define new classes, use global variables, etc.