I'd like to get an idea for data grouping.

[youngrap]

I have numeric data.
I'd like to group the data.
It is easy to use 'Kmeans' command, but it cannot be necessarily k=3.
I want to set k automatically.

Or Is there any other good idea to group?

ex)
53,752
53,731
53,699
10,427
10,437
110,854
111,054
111,001
...

result)

53,752	1
53,731	1
53,699	1
10,427	2
10,437	2
110,854	3
111,054	3
111,001	3
.....

[DalJeanis]

kmeans has an option for setting a range of ks to attempt.  

| kmeans k=3-12

Just feed it different data a few times and see what it does for you.  Here's the reference.

https://docs.splunk.com/Documentation/Splunk/8.0.4/SearchReference/Kmeans