Message-ID: <CAF8bMcaMQQQMDKtOGJVVi6x_yCsDXjK1mxKvC_B0nRxh+KS03g@mail.gmail.com>
Date: 2018-12-04T20:02:48Z
From: William Dunlap
Subject: order(decreasing=c(TRUE,FALSE),...)
The NEWS file for R-devel (as of 2018-11-28 r75702) says
? order(...., decreasing=c(TRUE,FALSE)) could fail in some cases.
Reported from StackOverflow via Karl Nordstr?m.
However, either I don't understand the meaning of decreasing=c(TRUE,FALSE)
or there are still problems. I thought order(x,y,decreasing=c(TRUE,FALSE)
meant to return indices, i, such that x[i] was non-increasing and that ties
among the x's would be broken by y in non-decreasing order. E.g., that
interpretation works for numeric vectors:
> d <- data.frame(X=c(2,1,2,1,2,2,1), N=c(4:7,1:3))
> d[order(d$X, d$N, decreasing=c(TRUE, FALSE)), ] # expect decreasing X
and, within group of tied Xes, increasing N
X N
5 2 1
6 2 2
1 2 4
3 2 6
7 1 3
2 1 5
4 1 7
But it fails for character vectors: E.g., add some of those that have the
same sort order as 'N':
> d$Char <- LETTERS[d$N]
> identical(order(d$N), order(d$Char)) # expect TRUE
[1] TRUE
I expected the new columns to give the same sort order when they replace
'd$N' in the first call to order, but they do not: It acts like it would
with decreasing=c(TRUE,TRUE).
> order(d$X, d$Char, decreasing=c(TRUE, FALSE))
[1] 3 1 6 5 4 2 7
> d[order(d$X, d$Char, decreasing=c(TRUE, FALSE)), ]
X N Char
3 2 6 F
1 2 4 D
6 2 2 B
5 2 1 A
4 1 7 G
2 1 5 E
7 1 3 C
Bill Dunlap
TIBCO Software
wdunlap tibco.com
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