Ignoring blank cells in an IF statement formula

I am trying to ignore blank cells in a certain column. Columns A and B contain data. Column A contains number between 2 and 11, and column B contains measured data.
The formula I am using is as follows:

{=VAR(AVERAGE(IF(A1:A100=2,B1:B100,"")),......}

This formula goes on using 2 to 11 in the logic test statement and takes the variance. But, if one of the cells is blank in the B column, an error occurs in the IF statement evaluation, leading to an error as the final answer.
This workbook will be used by others, and there is no way to predetermine which cells will be blank when data is pasted into the worksheet.

Thanks.

i cant get that bit to fail

{=AVERAGE(IF(A1:A100=2,B1:B100,""))}
filled b up with various numbers
and formula calculated the average of every value in b corresponding to 2 in col a
irrespective if col b had blanks either anywhere or in the same row as a 2 in a
but you do get a #div/0 error if no 2 present in col a

If you mean that you don't want blanks in column B included in the average as if they're zeroes then try

=AVERAGE(IF(A1:A100=2,IF(B1:B100<>"",B1:B100)))

Thanks for all your help. I did not want the blanks in column B included in the averages, as that would have thrown off the data. When I put in the final formula, I used the offset function and combined it with the count function since the amount of data will vary. I got an error saying that "The formula is too long" before I got done entering it. How long can a formula be? The data are in columns O and Q (used A and B as an expample). There has got to be an easier way to do this. It escapes me currently. See below.

{=VAR(AVERAGE(IF(OFFSET('2320 Data'!$O$3,0,0,COUNTA('2320 Data'!$O$3:$O$65536),1)=2,IF(OFFSET('2320 Data'!$Q$3,0,0,COUNTA('2320 Data'!$Q$3:$Q$65536),1)<>0,OFFSET('2320 Data'!$Q$3,0,0,COUNTA('2320 Data'!$Q$3:$Q$65536),1),""))),AVERAGE(IF(OFFSET('2320 Data'!$O$3,0,0,COUNTA('2320 Data'!$O$3:$O$65536),1)=3,IF(OFFSET('2320 Data'!$Q$3,0,0,COUNTA('2320 Data'!$Q$3:$Q$65536),1)<>0,OFFSET('2320 Data'!$Q$3,0,0,COUNTA('2320 Data'!$Q$3:$Q$65536),1),""))),AVERAGE(IF(OFFSET('2320 Data'!$O$3,0,0,COUNTA('2320 Data'!$O$3:$O$65536),1)=4,IF(OFFSET('2320 Data'!$Q$3,0,0,COUNTA('2320 Data'!$Q$3:$Q$65536),1)<>0,OFFSET('2320 Data'!$Q$3,0,0,COUNTA('2320 Data'!$Q$3:$Q$65536),1),""))),AVERAGE(IF(OFFSET('2320 Data'!$O$3,0,0,COUNTA('2320 Data'!$O$3:$O$65536),1)=5,IF(OFFSET('2320 Data'!$Q$3,0,0,COUNTA('2320 Data'!$Q$3:$Q$65536),1)<>0,OFFSET('2320 Data'!$Q$3,0,0,COUNTA('2320 Data'!$Q$3:$Q$65536),1),""))))}