On Aug 25, 2012, at 5:37 PM, darnold wrote:
All, I am looking at an example in Aliaga's Interactive Statistics.
Bag A has
the following vouchers.
BagA <- c(-1000,10,10,10,10,10,10,
10,20,20,20,20,20,20,30,
30,40,40,50,60)
Bag B has the following vouchers.
BagB <- c(10,20,30,30,40,40,50,50,
50,50,50,50,60,60,60,60,
60,60,60,1000)
Two values are selected (from BagA or BagB) without replacement. In
Table
1.1 on page 54 of the third edition, she lists all "Possible two
values
selected" in columns one and two,
?unique
?expand.grid or ?combn
Perhaps spliting names from the tabulation below>
the "Average of the two selected values"
?mean
in column three and "BAG A Numbers of way of selecting the two
values" in
column four, and "BAG B Number of ways of selecting the two values" in
column five.
Here are the first few rows:
-1000 -1000 -1000 0 0
Why is that combination even listed?
-1000 10 -495 7 0
-1000 20 -490 6 0
-1000 30 -485 2 0
-1000 40 -480 2 0
-1000 50 -475 1 0
-1000 60 -470 1 0
-1000 1000 0 0 0
What are the rules for listing a combination?
10 10 10 21 0
10 20 15 42 1
I can get that value if choosing just from BagA, but if the
possibilities are for either bag to be selected, then an additional
value would arise because 10 and 20 are in BagB.
?table
?apply
?paste
...
She then condenses the data in Table 1.2 on page 55, the first column
holding "Average of the two selected values', the second column
holding "BAG
A Number of ways of selecting the two values," and third column
holding "BAG
B Number of ways of selecting the two values."
Here are a few sample rows:
-1000 0 0
-495 7 0
-490 6 0
....
Can anyone help show me an efficient way of creating these two tables?
table( apply( combn(BagA,2), 2, function(x) paste( sort(x), sep=".",
collapse=".") ) )
table( apply( combn(BagB,2), 2, function(x) paste( sort(x), sep=".",
collapse=".") ) )
You should be able to take it from this illustration of how to get the
BagA results:
cbind( do.call( rbind ,
sapply(names(table( apply( combn(BagA,2), 2, function(x)
paste( sort(x), sep=".", collapse=".") ) ) ) , strsplit, split= "\
\.") ), # first 2 columns
table( apply( combn(BagA,2), 2, function(x) paste( sort(x),
sep=".", collapse=".") ) ) )
[,1] [,2] [,3]
-1000.10 "-1000" "10" "7"
-1000.20 "-1000" "20" "6"
-1000.30 "-1000" "30" "2"
-1000.40 "-1000" "40" "2"
-1000.50 "-1000" "50" "1"
-1000.60 "-1000" "60" "1"
10.10 "10" "10" "21"
10.20 "10" "20" "42"
10.30 "10" "30" "14"
10.40 "10" "40" "14"
10.50 "10" "50" "7"
10.60 "10" "60" "7"
20.20 "20" "20" "15"
20.30 "20" "30" "12"
20.40 "20" "40" "12"
20.50 "20" "50" "6"
20.60 "20" "60" "6"
30.30 "30" "30" "1"
30.40 "30" "40" "4"
30.50 "30" "50" "2"
30.60 "30" "60" "2"
40.40 "40" "40" "1"
40.50 "40" "50" "2"
40.60 "40" "60" "2"
50.60 "50" "60" "1"
--
David.
David Winsemius, MD
Alameda, CA, USA
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