Remove commas and format dates

I have a large file with entries such as:

<VAL>17,451.26</VAL>
<VAL>353.93</VAL>
<VAL>395.00</VAL>
<VAL>2,405.00</VAL>
<DATE>31 Jul 2013</DATE>
<DATE>31 Jul 2013</DATE>
<DATE>31 Dec 2014</DATE>
<DATE>21 Jun 2002</DATE>
<DATE>10 Jul 2002</DATE>
<MOD>PL</MOD>
<BATCH>13382</BATCH>
<TYPE>Invoice</TYPE>
<REF1>13541/13382</REF1>
<REF2>671042638320</REF2>
<NOTES>a-07 final elec</NOTES>
<SNAME>EDF ENERGY ( Electricity )</SNAME>
<VAL>55.22</VAL>
</CLT>
<CLT>
<CHD>MAT-01</CHD>
<OPN>U5U1</OPN>
<PERIOD>07 2013</PERIOD>
<DATE>13 Jun 2013</DATE>
<DATE>10 Jul 2002</DATE>
<DATE>10 Jul 2002</DATE>
<DATE>21 Aug 2007</DATE>
<DATE>10 Jul 2002</DATE>
<VAL>-4,122,322.03</VAL>

I need to remove the commas in the VAL fields and change the dates to YYYY-MM-DD (e.g. 2013-07-31) in the DATE fields.

Looking for a quick (efficient) way of doing this.

Thanks

Solution

sed '# init month convertor in holding buffer
1{h;s/.*/Jan01Fev02Mar03Apr04May05Jun06Jul07Aug08Sep09Oct10Nov11Dec12/;x;}

# change Val
  /^<VAL>/ s/,//g

# Change Date
  /^<DATE>/ {
# change month
    G
    s/[[:space:]]\{1,\}\([A-Z][a-z][a-z]\)[[:space:]]\{1,\}\(.*\)\n.*\1\([0-9][0-9]\).*/-\3-\2/
# reformat order
    s/>\(.*\)-\(.*\)-\(.*\)</>\3-\2-\1</
  }' YourFile

posix sed with not extra sub shell for dae conversion
reformat date take 2 s///here but could be merged in 1 s/// a bit more unreadeable (already very attractive regex like this)
could easily add some security feature about source date like bad date format