Arsthbt

I have a file called data whose contents are

id,col1,col2
0,-0.3479417882673812,0.5664382596767175
1,-0.26800930980980764,0.2952025161991604
2,-0.4159790791116641,-1.3375045524610152
3,-0.7859665489205871,-0.6428101880909471
4,-1.3922759043388822,-1.676262144826317
5,-1.2471867496427498,-0.4912119581361516
6,1.443385383041667,1.6974039491263593
7,-2.058899802821969,2.0607628464079917
8,-0.10641338441541626,0.035929568275064216
9,-0.517273684861199,-0.6184800988804992
10,-0.9934859021679552,1.0577312348984502
11,0.5923834706792905,-0.6693757541250825
12,0.8657741917554445,-0.6876271057571398
13,-1.2061097548360489,-0.7402582563022937
14,0.78768021182158,-0.38607117005262315

Sorting numerically (-n) on the first column gives

$ sort -nk1 -t"," data
0,-0.3479417882673812,0.5664382596767175
id,col1,col2
1,-0.26800930980980764,0.2952025161991604
2,-0.4159790791116641,-1.3375045524610152
3,-0.7859665489205871,-0.6428101880909471
4,-1.3922759043388822,-1.676262144826317
5,-1.2471867496427498,-0.4912119581361516
7,-2.058899802821969,2.0607628464079917
8,-0.10641338441541626,0.035929568275064216
9,-0.517273684861199,-0.6184800988804992
10,-0.9934859021679552,1.0577312348984502
13,-1.2061097548360489,-0.7402582563022937
6,1.443385383041667,1.6974039491263593
11,0.5923834706792905,-0.6693757541250825
12,0.8657741917554445,-0.6876271057571398
14,0.78768021182158,-0.38607117005262315

This absolutely bizarre to me. I read in the man page that -n is supposed to be numerical sort. Why would id be placed in-between numbers? How is it that 10 is larger than 9, but smaller than 6, all the while 11 being greater than them all?

The -g seems to work as I want (and as I think is natural), but this -n option totally escapes me. What's this about? I think it can be related to locale, but once I specify the delimiter as being ,, I don't think that would explain it.

In English locales, , is the thousand separator, which is ignored in numbers.

-k1 defines a key that starts with the first field, but as you didn't specify where it stops, ends at the end of the line, so the sort key is the full line, which is the default.

So sort -t, -k1 -n is exactly the same as sort -n. With , ignored, you're sorting on these numbers:

0
1
2
3
4
5
61.4433853830416671
7
8
9
10
110.5923834706792905
120.8657741917554445
13
140.78768021182158

Here, you want:

sort -t, -n -k1,1

To sort on the first , delimited field only.

You can also use sort -n in the C locale where , is neither the decimal radix nor the thousand separator (and . is the decimal radix):

LC_ALL=C sort -n