Better way for Grouping rows in a series.
Ged Byrne
After a long break I'm getting back into REBOL and I was wondering if
anybody could help me out with a few pointers on how to be more
REBOLious.
I'm using the following script to group data from a table.
It's pretty short, but I'm not happy with it. Can anybody recommend
improvements.
Thanks.
----
rebol[]
data: [
;Country Name
"UK" "John"
"US" "Bradley"
"UK" "George"
"US" "Cory"
"US" "Bret"
"UK" "Henry"
]
result: copy []
foreach country unique extract data 2 [
append result country
append/only result copy []
]
forskip data 2 [
append
select result first data
second data
]
probe result
----
The result is this:
[
"UK" ["John" "George" "Henry"]
"US" ["Bradley" "Cory" "Bret"]
]
Gregg Irwin
You might get a better response on the ML than here, but...
You could mod this for your needs. It expects the rows to be
sub-blocks, and it doesn't remove the column you're grouping by, but
it's a general solution. I think this was something I did early in my
REBOLing, so it could probably be greatly improved as well.
group-by: func [ ; See SPLIT
{Returns a block of blocks+sub-blocks with items partitioned by
matching index elements in each sub-block.}
block [any-block!] "A block of series values"
index [integer!] "Index of sub-series value to compare, for grouping."
/part "Compare part of the series, rather than a single value."
range [number!]
/local result val
][
result: copy []
either part [
; First, build up a list of keys, with empty blocks to go with each.
foreach item block [
val: copy/part at item index range
if not find/only/skip result :val 2 [repend result [:val copy []]]
]
; Find the correct place (key) to put an item, and add it there.
foreach item block [
val: copy/part at item index range
append/only select/only result :val item
]
][
; First, build up a list of keys, with empty blocks to go with each.
foreach item block [
val: item/:index
if not find/skip result :val 2 [repend result [:val copy []]]
]
; Find the correct place (key) to put an item, and add it there.
foreach item block [
val: item/:index
append/only select result val item
]
]
result
]
group-by [[a 1 2] [b 2 3] [a 2 4] [c 2 3] [b 1 5]] 1
group-by [[a 1 2] [b 2 3] [a 2 4] [c 2 3] [b 1 5] [c 2 4]] 2
group-by [[a 1 2] [b 2 3] [a 2 4] [c 2 3] [b 1 5] [c 2 4]] 3
group-by/part [[a 1 2] [b 2 3] [a 2 4] [c 2 3] [b 1 5] [c 2 4]] 1 2
group-by/part ["ABC" "AAC" "ABD"] 1 2
--Gregg
Oyster
thanx
Gregg Irwin
O> hi, Gregg, where is the mail-list and how can I join it?
See: http://www.rebol.com/discussion.html for details.
There is also an archive of old messages on REBOL.org.
--Gregg