Is it possible to export my library to excel, sorted by tag and first author? I would need each tag to be on a separate sheet on excel, sorted by author name, with title and year.
Zotero has basic CSV export (which you can open with excel and would be easily able to sort by first author) but no, you can't generate complex excel reports with separate sheets generated by user-selected criteria (tags, in your case). Don't think that'll happen, either, other than as a 3rd party plugin if someone wants to code it.
I'm fairly certain that, once you have your Zotero records imported to a single sheet, Excel can do what you need. It has very powerful means of manipulating data and moving parts of sheets from one tab to another. For example, I use this power to take imported material from multiple years; disaggregate the data by years while moving each year to a separate tab; then taking the journal title columm within each year's tab; compare the titles and produce listings of year-to-year comparisons of journal titles that are in one year but not in another.
I'll follow up this post soon with an example of the formula to achieve this.
=VLOOKUP(lookup value,table range, column number, false) --be sure to use absolute references for your table range or (perhaps better) create "name-range" so that you don't get lost.
Conditional styles The final step where I Compare a list in sheet 1 with a list in sheet 2, identify unique titles in each of the sheets and highlight in different colors the unique titles within each year--
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I'll follow up this post soon with an example of the formula to achieve this.
https://msdn.microsoft.com/en-us/library/6fczc37s.aspx
To move selected columns to new tabs use
=VLOOKUP(lookup value,table range, column number, false)
--be sure to use absolute references for your table range or (perhaps better) create "name-range" so that you don't get lost.
Conditional styles
The final step where I Compare a list in sheet 1 with a list in sheet 2, identify unique titles in each of the sheets and highlight in different colors the unique titles within each year--
Range: B1:B1048576,B1
Formula: COUNTIF(listA,B1)=0
Apply custom style: cell_colorA
Range: A1:A1048576,A1
Formula: COUNTIF(listB,A1)=0
Apply custom style: cell_colorY
EDIT--
Here is a screen shot of the final product:
https://dl.dropboxusercontent.com/u/29002616/product.png