Google Spreadsheet LOOKUP by Dynamic Value - google-sheets

Question

I am trying to figure out if it is possible to use LOOKUP function that is based on a dyanmic value. For example:
=LOOKUP("A", C$2:C$1000, B$2:B$1000)
The above will look for Letter A in C Column and then write the value from the corresponding B Column row. What I wish to do is now read the Letter A from the D column, like so:
=LOOKUP(D2, Sheet2!C$2:C$1000, Sheet2!B$2:B$1000)
However, the above gives me an error. Is there a way to accomplish the above?
The above keeps returning me with an error saying value not found, I'm not sure what I am doing wrong.
EDIT
Ok so I have been playing more with this and I started having some very strange results. Lets take the following table: https://docs.google.com/spreadsheets/d/1ki3pmCOQoI1DLcbjEO-uwgwZGFfnHhM-fodspw8v1Qs/#gid=1001637055
Then my second sheet is this:
https://docs.google.com/spreadsheets/d/1ki3pmCOQoI1DLcbjEO-uwgwZGFfnHhM-fodspw8v1Qs/edit#gid=1993578337
If you look at the second sheet, bob shows up multiple times and I don't understand why.

Answer 1

Reason for #N/A's
lookup produces #N/A if it is looking up an empty range as is the case here. `'Draft Options'!A:A is empty so lookup cannot find a value to look up against.
Reason for multiple appearances
The documentation states that:
The LOOKUP function will only work properly if data in search_range or
search_result_array is sorted. Use VLOOKUP, HLOOKUP, or other related
functions if data is not sorted.
If search_key is not found, the item used in the lookup will be the
value that’s immediately smaller in the range provided. For example,
if the data set contains the numbers 1, 3, 5 and search_key is 2, then
1 will be used for the lookup.
Now, you are looking up Text but the same thing applies, it needs to be ordered alphabetically.
This is because lookup is doing something called binary search
Since your data is unordered and (assuming you have column A filled with keys the following can happen which leads to weird results:
Lookup looks at the middle entry and checks if the value comes before or
after the lookup value in an alphabetically sorted list.
If it comes
before it checks the the entry int he middle between the beginning
of the list and the middle.
If your entry happens to be in the latter half lookup never finds this entry
or
This value might not exists so it picks the first value it can find that would come before that (assuming the data is sorted) or something (seemingly random) where lookup finds value n to be alphabetically after the lookup value and n+1 alphabetically before and returns value n+1.
You should only use lookup if you know the lookup values will be there and that they will be sorted. Otherwise you might want to take a look at VLookup or Index Match
Solution
If Column A in Sheet Draft options Actually contains those letters you are looking up you can use a simple VLookup:
=VLOOKUP(F2, `Draft Options`!$A$2:$B$1000, 2, FALSE)
Here FALSE specifies that VLookup shall not use a binary search algorithm and instead go through the list linearly (i.e. one by one) which is slower but will retrieve the first matching value or throw an error if it is not there instead of returning something odd.