How do you find the average of numbers in excel based on criteria in other cells? - excel

Question

I have a fair bit of data I am trying to make smaller. My data is arranged in minutes following an event with associated sugar readings (see below):
469 13.3
471
474 13.5
479 14.1
484 14.3
489 14.3
494 14
499 13.9
504 14.2
509 13.9
514 13.7
519 13.4
524 13.5
529 13.8
534 14.1
539 14.3
544 14.1
549 13.8
554 13.2
559 12.9
564 12.9
569 12.8
574 12.4
579 12.1
584 11.9
589 11.7
594 11.7
599 11.8
604 11.7
The minute readings go up to ~4500. I was wondering if there is a way to find the average of the sugar readings based on time criteria - e.g. find the sugar average for every 20 minute group. I also have time data as well if this helps (e.g. 10/12/2013 13:53)?
Thanks for your help!
Alternatively is there a way to add in numbers between the minute values with blank spaces between the sugar values - that is:
Instead of this:
469 13.3
471
474 13.5
479 14.1
484 14.3
It would be this:
469 13.3
470
471
472
473
474 13.5
475
476
477
478
479 14.1
480
481
482
483
484 14.3
Thanks again

Answer 1

I don't understand the first part exactly, but in general, you can use Excel's AVERAGE function:
=AVERAGE(A1:A10)
=AVERAGE(A:A)
The first one will output the average of the values between A1 and A10 (inclusive), the second one will output the average of all values in the A column.
In the second part of your question, you ask to "expand" the time values with the measurement values. This is best done in a second sheet. Let's name the sheet with the data you have Data.
In the second sheet, write 469 in A1, 470 in A2 and then you can drag it down to the final measurement time.
Then, in B1 (of the second sheet we just started working on), add the following:
=IF(ISNA(VLOOKUP(A1, Data!$A$1:$B$200, 2, FALSE)), "", VLOOKUP(A1, Data!$A$1:$B$200, 2, FALSE))
Drag it down all the way to the last measurement time. You might have to change the two references to $B$200 to something higher, like $B$500 or whatever the highest row number is in the original Data spreadsheet.
This will add the measurement value for the corresponding time from the Data sheet, or it will just be an empty cell if there is no such value (e.g. no value for time 472).
Some explanations to that formula (skip if not interested). The heart of the formula is the following:
VLOOKUP(A1, Data!$A$1:$B$200, 2, FALSE))
VLOOKUP searches for a value at another place and then returns that row. In this case, we want to find the value A1 in Data!$A$1:$B$200, which is Excel's way of writing "the table A1 to B200 in the sheet Data". The $ signs guarantee that the values will not be changed as we drag the formula down, since Excel will automatically update regular cell references such as A1 in the formula.
So this will search for A1 in that area of Data and it will return a row. 2 specifies what cell's value we want to use, which is the measurement time right next to the value we just searched for (e.g. we found 564 in Data but we want to get the corresponding value next to it, i.e. 12.9).
VLOOKUP is a little dangerous in that it uses approximate values by default, which the last FALSE parameter prevents. To quote from microsoft.com [Source]:
If an exact match is not found, the next largest value that is less than lookup_value is returned.
And we really don't want that in this case. (It beats me why this is the default behavior, to be honest.)
VLOOKUP with no approximate search returns #N/A for values it can't find, and we don't want that all over our spreadsheet. This is why we test the function first:
=IF(ISNA(VLOOKUP(...)), "", VLOOKUP(...))
In other words, if VLOOKUP returns #N/A, let's just write nothing (""); otherwise, let's write what VLOOKUP returns to us.