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, Append in Place Implemented

initial writing: 2003-07-17 last updated: 2004-03-19

The phrases abc=:abc,expression and abc=.abc,expression are now done in place if possible, reducing the amount of time required if done repeatedly. For append in place to be possible,

• There must be sufficient excess space in abc (this is not directly under user control).
• There must be no increase in the number of columns in abc .
• abc must not be “promoted” (e.g. from integer to floating point).
• The internal type must be one of Boolean, literal (one or two bytes), integer, floating point, complex, or symbol.

The following benchmark demonstrates that ordinary append takes quadratic time while append in place takes linear time.

append=: 3 : 0    
 z=. i.0
 for_i. i.y. do.
  z=. i,z        NB. not append in place
 end.
)

appendip=: 3 : 0
 z=. i.0
 for_i. i.y. do.
  z=. z,i        NB. append in place
 end.
)
 
ts=: 6!:2 , 7!:2@]   NB. time and space
ts 'append n'  

n		Append				Append in Place				Ratio
1000		0.014100		15040		0.010849		13056		1.30		1.15
2000		0.033592		27328		0.021497		23296		1.56		1.17
4000		0.082590		51904		0.044137		43776		1.87		1.19
8000		0.836611		101056		0.085612		84736		9.77		1.19
16000		3.763209		199360		0.174779		166656		21.53		1.20
32000		15.665998		395968		0.350860		330496		44.65		1.20
64000		66.094799		789184		0.689447		658176		95.87		1.20
128000		283.322519		1575616		1.394492		1313536		203.17		1.20

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