# Excel - IF Function Problem - Expert Solution

Question description:
This user has given permission to use the problem statement for this blog.

I'm trying to make a gant chart but with non-linear predecessors. Trying to make a formula if a predecessor is a task no. the start date of one task will be the end date of the predecessor. Can't figure out how to use the IF command for this
Solved by G. Y. in 19 mins
This is the chat thread from the real Excelchat help session. It contains no private user information.
Excelchat Expert 05/10/2018 - 06:31
Hi…Welcome to Got It Pro. I see that your question is about fixing IF formulas.
Excelchat Expert 05/10/2018 - 06:31
Excelchat Expert 05/10/2018 - 06:31
Before we get started, this is a quick reminder that our policy is 1 problem per session with additional Q&A on that problem as time allows.
User 05/10/2018 - 06:31
Hi! Thanks and no problem!
User 05/10/2018 - 06:32
will i fire together something to show the problem
Excelchat Expert 05/10/2018 - 06:32
Could you please share your file or a sample data in this preview sheet will be fine as well?
User 05/10/2018 - 06:33
yep give me 2 seconds
Excelchat Expert 05/10/2018 - 06:33
Sure
User 05/10/2018 - 06:34
my problem is i am trying to write a formula
User 05/10/2018 - 06:34
that the start date of each specific task is = to the finish date of another one
Excelchat Expert 05/10/2018 - 06:35
Excelchat Expert 05/10/2018 - 06:35
This will take me few minutes.
User 05/10/2018 - 06:35
ill keep plugging away
Excelchat Expert 05/10/2018 - 06:35
sure
User 05/10/2018 - 06:35
so far ive been using
User 05/10/2018 - 06:35
IF AND and MATCH to try and make it work
Excelchat Expert 05/10/2018 - 06:36
So basic rule is finish date of prior task must be start date for the following task, is that right?
User 05/10/2018 - 06:37
yep
User 05/10/2018 - 06:37
i can't use a simple reorder and make it previous cell as the overall sheet will be used by a group
Excelchat Expert 05/10/2018 - 06:37
I didn't get you.
User 05/10/2018 - 06:38
so normally I could just rearrange the tasks, to make it a simple formula
User 05/10/2018 - 06:38
but they will always be shuffled
Excelchat Expert 05/10/2018 - 06:38
So do you mean to say you are going to use predecessors as the identifier of the prior task?
User 05/10/2018 - 06:39
yep
Excelchat Expert 05/10/2018 - 06:39
I mean you will have that Column E to identify what was the prior task.
User 05/10/2018 - 06:39
or the identifier or the start date
Excelchat Expert 05/10/2018 - 06:40
Ok...let me build a formula and let's see if that works.
User 05/10/2018 - 06:40
so column B will depend on the finish date of the predecessor which is labelled in column D and given by column E
Excelchat Expert 05/10/2018 - 06:44
Could you please review the formula in B4 and down?
Excelchat Expert 05/10/2018 - 06:45
Does that work?
User 05/10/2018 - 06:45
Excelchat Expert 05/10/2018 - 06:45
Sure
Excelchat Expert 05/10/2018 - 06:45
I am using Index-Match function.
Excelchat Expert 05/10/2018 - 06:46
So the formula syntax is = Index(Table to index,row number, column index)
Excelchat Expert 05/10/2018 - 06:46
So I am using table as column A to E
Excelchat Expert 05/10/2018 - 06:46
And for row number, I am using Match function
Excelchat Expert 05/10/2018 - 06:47
So Match(value to match,lookup range,exact match)
Excelchat Expert 05/10/2018 - 06:47
Here value to lookup is the value in column E in the corresponding row.
Excelchat Expert 05/10/2018 - 06:48
lookup range is column A
Excelchat Expert 05/10/2018 - 06:48
0 is to indicate to return exact match
Excelchat Expert 05/10/2018 - 06:48
Then 4 is the column index from where we want the result.
User 05/10/2018 - 06:49
I understand
User 05/10/2018 - 06:49
thats pretty awesome
Excelchat Expert 05/10/2018 - 06:49
Since our table is from column A to E, and result that we want is from D, its a 4
User 05/10/2018 - 06:49
Thank you!
Excelchat Expert 05/10/2018 - 06:49
Perfect.
Excelchat Expert 05/10/2018 - 06:49
User 05/10/2018 - 06:50
im doing an advanced course in uni and wasn't aware of the index formula. I'll look up how to use it in greater detail
User 05/10/2018 - 06:50
thank you again for your help!
Excelchat Expert 05/10/2018 - 06:50
Index is very helpful and more flexible then vlookup
Excelchat Expert 05/10/2018 - 06:50
Excelchat Expert 05/10/2018 - 06:50
Thanks for your time. Please do come back for any new question. You can now end this session. Have a great day ahead!
User 05/10/2018 - 06:51
Ill leave some feedback! same to you!
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