Google Appscript partial vlookup - google-apps-script

Question

I am very new to appscript and any help on the below query will really be helpful.
I am having data in Sheet1 in column A and Column B, now I want to design an appscript which get the below job done.
(1) Sheet1 Column A has Roll number along with student name i.e. Roll No.*Name, column B has actual value (these both columns are user input).
(2) Sheet2 has two columns Roll No. and Dummy value.
(3) In Sheet1 column C, I want the dummy value from Sheet2 column B by matching the Roll number of both sheets, however, I want value only in those rows in which actual value (column B) in Sheet1 is blank.
For reference I am sharing the link of the sheets.
https://docs.google.com/spreadsheets/d/1vI22QCmixKe3aoWMLODTFzt7pNXIKO3pjXS4mT6GHT0/edit#gid=524973836
I had checked different question on this community but not found a solution to my query.
Any help on above will really be appreciated.
Regards

Answer 1

Assume you want to put down 'dummy values' in Sheet1 column C if column B is empty, and that so call 'dummy value' need to has its 'Roll No.' value matched with the number of the front part of 'Roll No.#Name' column in sheet1:
Solution - 1. in-app lookup function:
Put this code into Column C2 in sheet1.
This code lookup for matches of 'Roll No.' from sheet2 column A whenever there Column A is not empty and Column B is empty in sheet1.
=ArrayFormula(
IFS(
$A$2:$A="","",
$B$2:$B<>"","",
TRUE,XLOOKUP(INDEX(SPLIT($A$2:$A,"*"),,1),sheet2!$A:$A,sheet2!$B:$B)
)
)
Solution - 2. write a custom function in apps-script:
in-app call:
apps-script js code:
this solution create a custom function called 'MYLOOKUP()' with apps-script, and call the function form the spreadsheet.
// apps-script:
function MYLOOKUP(data1,data2) {
return data1
.map(([rollNo_Name,value]) => {
return (rollNo_Name !== '' && value === '') ?
data2.find(([rollNo,]) => rollNo_Name.split('*')[0] == rollNo)[1] :
''
});
}
in-app call:
=MYLOOKUP(A2:B,sheet2!A:B)
There are a lot other solution to your question if you mention apps-script, such as...
instead of calling the custom function in-app, you can instead create a custom menu to run the function when you click on it,
or add simple trigger so that every time the spreadsheet is edited, the function will be run one time.
you can even create a web ui for this thing to run, etc.