Subject: Re: Finding non-common elements in two arrays
Bruce A. Pokras wrote:
The intersect function will return the common elements of two
arrays. Is there any array methodology that will return the
non-common elements of two arrays? I download a government list
each month, and I would like an easy way to spot the records that
are either new or changed. Currently, I use a repeat structure to
go through the old list line-by-line to see if any lines are not
identically found in the new list (using offset), and collect a
third list of any lines in which offset=0. After splitting the old
and new lists into arrays, an "inverse-intersect" function or
equivalent would seem to be a more elegant way of doing this.
Any ideas?
Thanks for everyone's the suggestions. I put Alex Tweedly's array
script (see below) to the test against a line-by-line "offset" script
("repeat for each line n in list1" etc.). The lists were text files
representing two consectutive months of a 20,000 line government
database with 11 fields per line. The idea is to see which records in
the new list have been added to or changed from the previous list.
There was simply no comparison between the methods. It took all of
18-19 seconds to make the comparison using Alex's method (I ran it
twice to make sure I wasn't imagining it). Using the line-by-line
offset method, it took 14 minutes! A comparison in MS Word of the
results of each method showed them to be identical.
I never would have believed that the first steps of going through
each list and creating complete copies of them with the tab & 1 or 2
could occur so quickly. The incredible speed of those two steps
(creating two new 20,000 line lists) is really what makes this thing
work.
I will next check out Wouter's more sophisticated version, since I
may have a use for the additional functionality of that one, also.
Thanks very much Alex and Wouter, and thanks to everyone else who
repsonded to my question.
Regards,
Bruce Pokras
Blazing Dawn Software
www.blazingdawn.com
on mouseUp
put fld "F1" into t1
repeat for each line L in t1
put L & TAB & "1" & cr after tA1
end repeat
split tA1 by CR and TAB
put fld "F2" into t1
repeat for each line L in t1
put L & TAB & "2" & cr after tA2
end repeat
split tA2 by CR and TAB
union tA1 with tA2
combine tA1 with CR and TAB
filter tA1 with ("*"&TAB&"2")
put tA1 into fld F3
end mouseUp
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