Sorting on a column alphanumerically - sorting

Question

I have following file and I want to sort it alphanumerically based on 6 th column such that an E1 is followed by I1 and then E2 and so on of a specific ID before the ' : ', when I do sort -V -k6 file it puts all the ID:Is at the end and not where they should be.However when I do sort -k6 it does put the Es and Is of the IDs together but with some IDs belonging to different series interspersed (I have highlighted them here), how can I get the sorting such that no two IDs are mixed and the column is in the order it should be:
chr1 259017 259121 104 - ENSG00000228463:E2
chr1 259122 267095 7973 - ENSG00000228463:I1
chr1 267096 267253 157 - ENSG00000228463:E1
chr1 317720 317781 61 + ENSG00000237094:E1
chr1 317782 320161 2379 + ENSG00000237094:I1
chr1 320162 320653 491 + ENSG00000237094:E2
chr1 320654 320880 226 + ENSG00000237094:I2
chr1 320881 320938 57 + ENSG00000237094:E3
chr1 320939 321031 92 + ENSG00000237094:I3
chr1 321032 321290 258 + ENSG00000237094:E4
chr1 321291 322037 746 + ENSG00000237094:I4
chr1 322038 322228 190 + ENSG00000237094:E5
chr1 322229 322671 442 + ENSG00000237094:I5
chr1 322672 323073 401 + ENSG00000237094:E6
chr1 323074 323860 786 + ENSG00000237094:I6
chr1 323861 324060 199 + ENSG00000237094:E7
chr1 324061 324287 226 + ENSG00000237094:I7
chr1 324288 324345 57 + ENSG00000237094:E8
chr1 324346 324438 92 + ENSG00000237094:I8
chr1 324439 326514 2075 + ENSG00000237094:E9
**chr1 326096 326569 473 + ENSG00000250575:E1**
chr1 326515 327551 1036 + ENSG00000237094:I9
**chr1 326570 327347 777 + ENSG00000250575:I1**
**chr1 327348 328112 764 + ENSG00000250575:E2**
chr1 327552 328453 901 + ENSG00000237094:E10
chr1 328454 329783 1329 + ENSG00000237094:I10
**chr1 329431 329620 189 - ENSG00000233653:E2**
**chr1 329621 329949 328 - ENSG00000233653:I1**
chr1 329784 329976 192 + ENSG00000237094:E11

Answer 1

Original answer:
sed 's/:[EI]/&_ /' foo.txt | #separate the number at the end with a space
sort -k6 | sort -n -k7 | #sort by code, then by [EI] number
sed 's/_ //' #remove the underscore space
I like to do things like this by 'protecting' strings with a placeholder to isolate what I'm interested in, then replacing them later.
Closer:
sed 's/:[EI]/_ &_ /' foo.txt | sort -n -k8 | sort -k6,6 | sed 's/_ //g'
But this naively assumes that sort works in a very specific way that it doesn't... so sometimes E2 will come before E1...
I'm not sure it can be done with sort alone, awk might be the way to go...

Answer 2

So I came back to this question and wrote some python code that actually accomplishes the task:
#!/usr/bin/env python
import sys
import re
from collections import defaultdict
#loop through args
for thisarg in sys.argv[1:]:
#initialize a defualt dict
bysign = defaultdict(list)
#read the file
try:
thisfile = open(thisarg,'r')
for line in thisfile:
#split each line by space and colon
dat = re.split('[ :]*',line.strip())
#append line to dictionary indexed by ENSG code
bysign[dat[-2]].append(line.strip())
thisfile.close()
except IOError:
print "no such file {:}".format(thisarg)
#extract the keys from the dictionary
mykeys = bysign.keys()
#sort the keys
mykeys.sort()
for key in mykeys:
#initialize another, smaller dictionary
bytuple = dict()
#loop through all the lines that have the same ENSG code
group = bysign[key]
for line in group:
#extract the E/I code
ei=line.split(':')[-1]
#convert the E/I code to a (char,int) tuple
letter = ei[0]
number = int(ei[1:])
#use that tuple to index the smaller dict
bytuple[(letter,number)] = line
#extract the keys from the sub-dictionary
eikeys = bytuple.keys()
#sort the keys
eikeys.sort()
#print the results
for k in eikeys:
print bytuple[k]
I hope you already figured it out by now. Curious if anyone cares enough to improve my python.