Noah Silverman ha scritto:
I only have a few values in my example, but the real data set might
have 20-100 rows with A="X". So how do I pick just the three highest
ones?
-N
On 8/26/09 2:46 AM, Ottorino-Luca Pantani wrote:
df.mydata[df.mydata$A=="X" AND df.mydata$C < 2, ]
will do the job ?
8rino
Noah Silverman ha scritto:
Hi,
I'm trying to find an easy way to do this.
I want to select the top three values of a specific column in a
subset of rows in a data.frame. I'll demonstrate.
A B C
x 2 1
x 4 1
x 3 2
y 1 5
y 2 6
y 3 8
I want the top 3 values of B from the data.frame where A=X and C <2
I could extract all the rows where C<2, then sort by B, then take
the first 3. But that seems like the wrong way around, and it also
will get messy with real data of over 100 columns.
Any suggestions?
my.data <- cbind.data.frame(expand.grid(A = c("X", "Y"), B = 1:100), C
= rnorm(100))
myA.data <- my.data[my.data$A == "X", ]
myA.sorted.data <- myA.data[order(myA.data$C, decreasing=TRUE), ][1:3.]
Do this solve your problem ?
--
Ottorino-Luca Pantani, Università di Firenze
Dip. Scienza del Suolo e Nutrizione della Pianta
P.zle Cascine 28 50144 Firenze Italia
Tel 39 055 3288 202 (348 lab) Fax 39 055 333 273
olpant...@unifi.it http://www4.unifi.it/dssnp/
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