Tcl Source Code

~ Prototype

lgroup listIn lengthOfSublist ?stepForward?

stepForward defaults to $lengthOfSublist

~ Example

set l {a b c d e f g h}
lgroup $l 4 # {a b c d} {e f g h}
lgroup $l 3 # {a b c} {d e f} {g h}
lgroup $l 1 # a b c d e f g h
lgroup $l 0 # {a b c d e f g h}
lgroup $l -1 # error
lgroup $l 3 2 # {a b c} {c d e} {e f g} {g h}
lgroup $l 2 3 # {a b} {d e} {g h}

~ Usefulness

This can be used to rearrange results returned by SQLite3.

~ Incomplete implementation

Since I just use it to process what SQLite3 returns, I have ignored the "stepForward". I think rewrite it in C will speed it up. I didn't check whether $lengthOfSublist is a negative number or zero.

proc lgroup {listIn lengthOfSublist} {
	set i 0
	foreach it $listIn {
		lappend tmp $it
		if {[llength $tmp] == $lengthOfSublist} {
			lappend result $tmp
			set tmp {}
		}
		incr i
	}
	if {[llength $listIn] % $lengthOfSublist} {
		lappend result $tmp
	}
	return $result
}

Don't worry about getting performance or the C implementation. Worry about <i>why</i> and <i>what</i> (i.e., a clear justification for this command and an exact specification of the behaviour).