Another related question to averaging previous values

[Speedy]

Still the same table as previous but with an additional col which is now
colA. ColA makes a 3-month analysis to the data such that now I would like to
find the mean of still the previous 6 months but "previous" based on colA not
on colB but still using the monthly numeric values in colB, just that the
definition of previous has changed, such that the average of previous six
months for cell D1 would be 1930jul,aug,sep,oct,nov,dec, cell D2
1930oct,nov,dec,1931jan,feb,mar, cell D3 1931jan,feb,mar,apr,may,jun and so
on until we get to end. I do have monthly values (in colB) prior to 1931jan I
thought putting them in doesn't look neat and may cause confusion. Over to
you with my many thanks for your help.

colA colB colC colD
1931jfm 1931jan 2 D1=mean previous 6 values based on
A(1930j,a,s,o,n,d)
1931amj feb 3 D2=mean (1930o,n,d,1931j,f,m)
1931jas mar 4 D3=mean (1931j,f,m,a,m,j)
1931ond ... ..
1932jfm .... ..
..... ..
1976ond 1976dec 5


Speedy

 

[Speedy]

Probably my question is not clear so I'm trying to post it again. I have 3
cols such that they look like this:

colA colB colC colD
1931jfm 1931jan 1 mean of 1930(j,a,s,o,n,d)
1931amj 1931feb 2 mean of 1930(o,n,d),1931(j,f,m)
1931jas 1931mar 3 ....
1931ond 1931apr 4 .....

where j is jan, f is feb, m is march and so on
1930(j,a,s,o,n,d) is jul1930, aug1930,sep1930 and so on till dec1930
I want to calculate the mean of the previous 6 months which is to become
colD. Because the columns are so long and many of them it's hard to do it
manually.

Many thanks again

Speedy
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