Ngayee J Law wrote:
Hi all,
I am trying to run the k-means cluster analysis using the function kmeans
in the package cluster.
The data are:
x = c(-0.26, -0.23, -0.05, -0.20, 0.30, -0.84, -0.10, -0.12, 0.10, -0.31,
-0.19, 0.18, -0.26,
-0.23, -0.37, -0.23)
I've got two different solutions when I ran this function over a few times:
kmeans(x, centers=2)
The first solution gives the following:
$cluster
[1] 2 2 1 2 1 2 2 2 1 2 2 1 2 2 2 2
$centers
[,1]
1 0.1325000
2 -0.2783333
$withinss
[1] 0.0646750 0.4033667
$size
[1] 4 12
The second solution gives the following:
$cluster
[1] 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1
$centers
[,1]
1 -0.1313333
2 -0.8400000
$withinss
[1] 0.5035733 0.0000000
$size
[1] 15 1
I don't understand why this is happening, and how do I choose between the
two solutions. Also, how can I ensure
consistent solution over times? Thanks a lot!
- Jacqueline
From the help page for `kmeans':
centers: Either the number of clusters or a set of initial cluster
centers. If the first, a random set of rows in `x' are chosen
as the initial centers.
If you want the same results try supplying an initial center, as in:
kmeans(x, centers = c(0.1, -0.2))
However, choosing bad starting values could cause kmeans to crash, as in:
kmeans(x, centers = c(0, 0))
Regards,
Sundar
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