R help - Jan 2012 - Aggregate by minimum

For each date, I would like to keep the line with the lowest speed and discard
the rest.  The result would have one line for each date.  Can I use aggregate
for this?

My table is as follows:
structure(list(speed = c(3,9,14,8,7,6), result = c(0.697, 0.011, 0.015, 0.012,
0.018, 0.019), house = c(1,
1, 1, 1, 1, 1), date = c(719, 1027, 1027, 1027, 1030, 1030), 
    id = c("1000", "10000", 
    "10001", "10002", "10003",
"10004")), .Names = c("speed",
"result", "house", "date", "id"), class
= "data.frame", row.names = c("1000",
"10000", "10001", "10002", "10003",
"10004"))

Thanks,
Jeffrey

 		 	   		  
	[[alternative HTML version deleted]]

try this:
> x <- structure(list(speed = c(3,9,14,8,7,6), result = c(0.697, 0.011,
0.015, 0.012, 0.018, 0.019), house = c(1,
+ 1, 1, 1, 1, 1), date = c(719, 1027, 1027, 1027, 1030, 1030),
+    id = c("1000", "10000",
+    "10001", "10002", "10003",
"10004")), .Names = c("speed",
+ "result", "house", "date", "id"),
class = "data.frame", row.names = c("1000",
+ "10000", "10001", "10002", "10003",
"10004"))
>
> require(plyr)
> ddply(x, .(date), .fun = function(a){
+     a[which.min(a$speed), ]
+ })
  speed result house date    id
1     3  0.697     1  719  1000
2     8  0.012     1 1027 10002
3     6  0.019     1 1030 10004
>
>
On Mon, Jan 9, 2012 at 8:23 PM, Jeffrey Joh <johjeffrey at hotmail.com>
wrote:
>
>
>
>
> For each date, I would like to keep the line with the lowest speed and
discard the rest. ?The result would have one line for each date. ?Can I use
aggregate for this?
>
> My table is as follows:
> structure(list(speed = c(3,9,14,8,7,6), result = c(0.697, 0.011, 0.015,
0.012, 0.018, 0.019), house = c(1,
> 1, 1, 1, 1, 1), date = c(719, 1027, 1027, 1027, 1030, 1030),
> ? ?id = c("1000", "10000",
> ? ?"10001", "10002", "10003",
"10004")), .Names = c("speed",
> "result", "house", "date", "id"),
class = "data.frame", row.names = c("1000",
> "10000", "10001", "10002", "10003",
"10004"))
>
> Thanks,
> Jeffrey
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

On Mon, Jan 9, 2012 at 8:00 PM, jim holtman <jholtman at gmail.com>
wrote:
> try this:
>
>> x <- structure(list(speed = c(3,9,14,8,7,6), result = c(0.697,
0.011, 0.015, 0.012, 0.018, 0.019), house = c(1,
> + 1, 1, 1, 1, 1), date = c(719, 1027, 1027, 1027, 1030, 1030),
> + ? ?id = c("1000", "10000",
> + ? ?"10001", "10002", "10003",
"10004")), .Names = c("speed",
> + "result", "house", "date", "id"),
class = "data.frame", row.names = c("1000",
> + "10000", "10001", "10002",
"10003", "10004"))
>>
>> require(plyr)
>> ddply(x, .(date), .fun = function(a){
> + ? ? a[which.min(a$speed), ]
> + })
Or even more succinctly:

ddply(x, .(date), subset, speed == min(speed))

Hadley


-- 
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/