In April 2011, Mdsuhair asked a question at the Chandoo.org Forums
This is a candidate for Solver.
This post will walk us through the solution to the problem using Solver. It uses Solver and screen shots from Excel 2007.
All versions of Excel have solver available. Users should note that the screen shots may not match your version although the functionality will, some of the functions appear in different locations in different versions of Solver.
What and Where Is Solver
What is Solver
Solver is an Excel add-in that can solve problems by enabling a Target cell to achieve some goal.
This goal may be to minimse, maximise, or achieve some target value.
It solves the problem by adjusting a number of input cells according to a set of criteria or constraints which are defined by the user.
Where is Solver
Solver is an Excel add-in supplied with Excel, but not enabled by default.
To enable solver
File, Excel Options, Add-ins, Manage Excel Add-ins, Select the Solver Add-in checkbox
Solver will now appear as a New Tab on the Data, Analysis Tab
Solver Example
This post is based around a worked example Solver Example File, the file is compatible with all versions of Excel.
Defining the Problem
Mdsuhair had a series of 8 Items each which had a value:
He wants to know which items should be combined so that the sum of the values of the items is nearly equal.
To do this we need to assign each item into a Bucket. Namely Bucket A and Bucket B.
We will put values of 1 into a Bucket for each Item to show that it is assigned to that Bucket and a value of 0 to show that the bucket is empty (In/Out) Value.
We can start by adding a Total Column, which counts items in Buckets A + Bucket B for each Item, It then totals the totals.
We also know that we need to work out the Value of each Item in each Bucket
We do this by multiplying the Items Value by the Buckets (In/Out) value
Finally we need to add up the values in each Bucket and work out the difference between them
Mdsuhair’s original problem was to minimise the difference between the sum of the values in the 2 buckets.
Now we can place values of 1 in the buckets manually and Excel will show us the value of each Bucket and the Difference between them in Cell G11.
I have applied some conditional formatting to show when a cell has a value > 0.
The problem is that there are 28 or 256 combinations of answers, and to test them all manually at 1 every 5 seconds would take 21.3 minutes, assuming we can keep up that pace and remember which was the best combination.
This is where solver comes to the fore.
Applying Solver
To apply solver we need to define a series of requirements, rules and constraints.
These requirements, rules and constraints guide solver and set limits which allow solver to quickly narrow in on the answer.
What are our rules
Our main requirement is to minimise the difference between the value of the 2 buckets.
The difference between the 2 buckets in our example is cell G11, the sum of Bucket 2 values minus the Sum of Bucket 1 values.
We want to have G11 as low as possible but greater than or equal to 0.
We also know that an item can only be in Bucket A or Bucket B, it can’t be in both and can’t be Broken apart.
That is 2 Constraints for each Item
Firstly The Total column must be equal to 1
Secondly the Buckets Values must be Integers
We also know that the Total Number of Items is 8, this is another constraint.
We will discuss how these constraints are used in the next section
The Solver Window
This section will explain the solver window and its use in defining the problem within solver.
A Blank Solver Window
A Filled Solver Window
Set Target Cell:
This is the Target cell which is the cell which you are trying to solve the problem for.
Our Target cell is G11, The difference between the 2 Buckets values
Equal To:
The Equal To: section defines what we want to do with our Target Cell.
We want to achieve the same value in each Bucket and so the difference between the Buckets will be 0.
It might sound strange but we don’t want to minimise that difference. A minimal value will be achieved when all the Items are placed in Bucket A, as our equation for G11 will then have 0 – Total which is –Total, which is more minimal than 0.
Another way to constrain this is to Change G11 to =Abs(G10-H10)
This allows us to use Min as an Equal To: Value
But for now we can just leave G11 as =G10-H10 and we will set the Equal To: section as 0.
By Changing Cells:
Changing Cells: refers to the cells which will be modified by Solver to try and solve the problem.
We want to let Solver change the number of items in each bucket, this is the range: $C$2:$D$9
Hint: You can try the Guess button next to the Range Reference and Solver will take a Guess at what cells the problem is dependent on.
Always check this if you use it, especially in complex models.
Subject to the Constraints:
Constraints are the rules which define the limits of the possible solutions to the problem
We will add several constraints for our rules:
1. The Total column must be equal to 1 for each Item
2. The Bucket Value must be an Integer
3. The total contents of the 2 buckets must be 8 items
4. You could add a further constraint that each Bucket should hold the same number of items
Hint: As a general Rule, Under Constrain rather than over constrain! You can always add more constraints later.
To do this we will use the Add Constraint Button
1. We need to add a constraint for each cell in the Range E2:E9 that it is only allowed to be = 1
This constraint must be applied for each cell in the range E2:E9
2. We need to add a constraint for each cell in the Range C2:D9 that it is only allowed to be an integer
This constraint must be applied for each cell in the range C2:D9
3. We need to add a constraint for the Total of the 2 Buckets, E10=8
You can Change or Delete Constraints if you make a mistake by selecting the appropriate constraint and using the Change or Delete Buttons
Save and Load Solves Parameters
Selecting the Options Button there is the Option to Save Model and Load Models.
Hint: The Save/Load Models has been shifted onto the main Solver dialog in Excel 2010.
Using the Save Model and Load Model options you can Save and the Load the Solver Parameters for your model. The Save Model saves the parameters in a Range of cells as shown below.
This allows an easy way to actually setup and/or change the solver parameters.
Hint: Setup one constraint using solver then Save the model. Edit the model on the worksheet and re-load the model as required.
Note: That the parameters although when saved show as True/False or Numbers are all Excel Equations, see above.
This means you can edit them to change the Constraints and Parameters as required and re-load them into solver.
I have included 3 sets of Parameters for our model.
These are:
- Base Case – Forces bucket values to be equal, Allows uneven bucket counts
- Equal Sized Buckets – Forces each bucket to contain the same number of items
- Force an error – Which forces an error in the solver model
Load each model and try them at your leisure.
Running the Solver Model
Warning: Solver is a computationally complex add-in, so once your model is setup, Save your Workbook.
Prior to running the model there are a few parameters we should look at to ensure the model solves correctly.
On the main Solver window select the Options button. (Some of these parameters are on the Main Solver window in Solver 2010)
Generally you can accept the defaults but in this case we will change the following
Assume Linear Model – Select
Assume Non-Negative – Select
Note: Solver in Excel 2010 will return a better answer without these 2 parameters enabled by default
The other 2 parameters which you may need to change from time to time is
Precision: Precision is a number from 0 to 1 and higher means more precise
Tolerance: Tolerance shows how far away from a Number, an Integer constraint is allowed to be
The use of the Estimates, Derivatives and Search parameters are beyond the scope of this post. I direct you to the Excel Help on these subjects, by selecting the Help button.
Run the Model
To Run the Model, select the Solve Button from the main Solver menu.
The main status bar in Excel will flash up a number of statistics about the internal workings of the Solver add-in. Generally these flash by and are too fast to read. If a model is too complex it may stall and you won’t see any movement for a while. Solver generally recovers from these problems itself.
Once the Solver model finishes it will display a dialog of the results and allow you to do several things
First thing to note is that “Solver Found a Solution“.
If it has found a solution, the worksheet cells will be changed to show the solution
You now have 4 options:
- Run a Report
- Save a Scenario
- Return to the model
- Check Your Results
Run a Report
Run a report by clicking the report you want.
A new sheet will be added to your workbook depending on the report but will be called:
- Answer Report 1,
- Sensitivity Report 1
- Limits Reports 1
etc.
Note, that not all reports are relevant at all times, depending on the Constraints you have applied.
Save a Scenario
Selecting the Save a Scenario button takes you to the Save Scenario dialog.
Type in a Name and the Scenario of your model is saved as a Scenario.
Scenarios as available for use in the Scenario Manager, which is accessed from the Data, What-If-Analysis Tab
Return to the model
You can return to your model and either:
- Keep Solver Solution
- Restore Original Values
Check the Results
Solver is probably the most Black Box’ish of systems within Excel. As such any results it puts out must be manually checked for suitableness before further use.
These checks for realness, should as a start confirm that the results meet all the criteria supplied.
Are the results roughly what were expected?
Are any Minimums or Maximums violated?
What If Solver Doesn’t Find a Solution?
From time to time Solver will return with an error that a “Solver could not find a feasible solution.”
When this happens it is indicating one of several possibilities:
- Your model is over or under constrained
- Your model constraints are impossible to meet
- Your model constraints have an error
Start by checking the current constraints for errors and ambiguities
Eg: in our case we have 8 items so requiring the Count of the two buckets to be 20 is impossible to meet
My Solver Answer has Strange Numbers?
In solver up to and including Excel 2007, solver would commonly return numbers like 3.5E-18.
This is 0.0000000000000000035, which is effectively 0
If your model returns these, feel free to go through the model and change them to 0, in our model we should also check as the corresponding 1, may in fact be 0.9999999999999999965.
It should be noted that this problem in Solver in Excel 2010 does not occur as often but will still occur.
What and How have you used solver in the past?
What and How have you used solver in the past?
Let us know in the comments below:
37 Responses to “Quickly Change Formulas Using Find / Replace”
Chandoo,
this is a really cool stuff what I use quite often. In addtion this method also could be a good choice to switch the reference type of the formulas from relative to absolute or vice versa. (just simply replace the $ in the same way).
Andras
@Andras: you are right, we can use find / replace to change references, reference types etc. Now, only if they had regex in find/ replace, we could so much more 🙂
@Tony Rose: Thank you. This is very useful and powerful feature. I even use it for cleaning up data. While formulas are good, they are not the solution for every problem. Often when I need more powerful cleanup / changing, I copy paste the stuff to text editors like notepad++ and then use their find/replace to do the dirty task.
What if i have to change the formula from ='Analysis'!C1 to 'Analysis 1'!C1?
I tried doing it using Find /Replace but could't. Encountered some errors.
And is there a way to change this using VBA???
Hi,
Did you ever get a reply to this?
Thanks
Ollie
to make your life easier, suggest you to avoid (Space) in worksheet names whenever possible. Consider (underscore) instead.
As the first formula wouldn't have the single apostrophes (since there's no space) need to include that in replace. So, search for:
Analysis
and replace with:
'Analysis 1'
This could be the most useful tips I've seen in a while. I use this all the time and can instantly change 400 formulas with a few clicks. Like so many other functions in Excel, I don't know what I would do without this one.
Keep 'em coming!
[...] on formulas: 5 areas where mouse kicks keyboard’s butt | Edit formulas in bulk using Find / Replace | Excel Formulas Online [...]
THANKS BRO
You, sir, are a god among men...
This is really cool. Your just save me hours of work. Thanks.
Thanks so much for this fix! It saved me tons of work. I'm muddling my way through and this really helped!
Oh... My... God!
This tip just saved me about 2 hours every month! I can't believe how easy it is to use. Now, can somebody tell me who I should call to get a refund for the previous 100 hours I spent manually changing formulas cell by cell?
Thanks so much!
THANK YOU!!!
THANK YOU!!!!
You saved me hours, I had a sheet that has more than 500 formulas, and i needed to replace the year in all of them, you saved me hours
Awesome info on replacing cell addresses in formulas. I have never heard about Ctrl+` before. Thank you!
I have something inside a formula like:
=sum(A1, A2*10) all over I now need to get rid of the *10 {=sume(A1, A2)} I thought to use the find replace trick above but with a blank in the replace but it then outputs just zeros. I thought I could trick it by doing *1 but then it just turns into =*1) with none of my references. Does anyone have an idea how to do this?
The Ctrl+ trick is cool.
@T
Instead of replacing with a blank try replacing
*10)
with
)
Thank you! This literally will save me hours and hours of time, and that's without losing my sanity in the process!
I have Sheet(1), Sheet(2), Sheet(3), etc ... Sheet(100).
Then there's a summary tab where I want to recap information on all those different sheets. Is there anyway to create a formula on the Summary tab to get ='Sheet(1)'!B$29 copied down for all 100 sheets without having to change each sheet # within the formula by hand?
@Brigitte
If you have a list of the sheet names in A2:A100
In B2: =INDIRECT("'"&A2&"'!$B$29")
Copy down
or if you don't have a list of the sheets names you can make it up on the fly
=INDIRECT("'sheet("&ROW()-1&")'!$B$29")
Copy down
Thanks for the suggestion. However, I copied your formula right back to my file and it didn't work. So I did it another way. I put the tab/cell reference in one cell and then did an =INDIRECT() to capture that information.
K2="'Sheet("&L2&")'!B$29" which has a value of 'Sheet(1)'!B$29
B2=INDIRECT(K2) which now has a value of 40 (contents on Sheet(1).
Thank you!!!!
Thank you ..
Hi, Out of all the formulae, I wish to replace the formula which has generated 0 value with blank space? I am unable to do it with find and replace function,
Please suggest.
Thanks.
Chandoo, you literally just saved me about 2 hours of work. I had a document with a daily report in two formats. The second formate just linked to all the appropriate cells in the other format (different sheets). This was 180 references that needed to be changed and I had to make this for a 4 week period (aka 28 different sheets at 180 references to change per sheet).
Thanks so much.
I have tried this way and without using the Ctrl-` formula view
Either way, I am trying to do something simple, but it won't let me.
I have a bunch of cells with a simple math formula like
=-(0.5*20)
various values in each cell, multiplied by 20
I simply want to change the multiplier globally from 20 to 25. But when I tell it to find *20 and replace it with *25, it replaces the entire cell contents with *25, rather than just replacing the *20 portion of the cell contents.
Can anyone assist with this? Seems so simple, but Excel isn't letting me do it.
Search/Replace 20 or 20) with a cell Reference eg A1 or A1)
Then put the value 25 in A1
By using a * in the search it replaces all the text
how to find a specific cell's value in a column & replace replace it with another cell value i actually need a method to replace a data in ca column and replace with the value i have in a specific cell can i give a [ location ] of data to what i need to find and then give row or column range to where i need to find and the given value & then give a [ location ] of data to what i want to be replace with the find and replace by row & column range & than by specific criteria and than by specific location.
please help.
how to find a specific cell’s value in a column & replace replace it with another cell's value.
i actually need a method to find a specific cell's data in a column and replace it with the value i have in a specific cell.
can i give a [ location ] of data to what i need to find and then give row or column range from where i need to find the given value & then give a [ location ] of data to what i want to be replace with.
find and replace by row & column range & than by specific criteria and than by specific location.
please help.
how to find a specific cell’s value in a column & replace it with another cell’s value.
i actually need a method to find a specific cell’s data in a column and replace it with the value i have in a specific cell.
can i give a [ location ] of data to what i need to find and then give row or column range from where i need to find the given value & then give a [ location ] of data to what i want to be replace with.
"find and replace by row & column range & than by specific criteria and than by specific location."
in more than 100 sheets in entire workbook
please help.
This is a great tool, does anyone knows an easiest way??
I'm working with a system that has over 59000 references... so every time the replace all is activated. I lose an entire day.
i actually needs to find cell number "D12" in column "D" and replace with Cell Number "B8" for example
find what = Cell Number "D12" John McNamara
find Where = in Column "D"
Replace with = Cell Number "B8" Bieber D'Souza
Replace Range = Column "D"
In which Sheet = All Sheets in Work Book (more than 100 Sheets)
Note: in every Sheet Cells Number "D12" & "B8" containing Different Employ Name but the find rang and replace rang are same in every sheet and find what cell number and replace with cell number are same also.
please help!
thank you. saved lot of time.
Thank you from the bottom of my heart!
Hi, I am trying to figure out how to use RE to find and replace several values in a column. Using find and replace does not work because of the values I am working with. I have a column with hundreds of rows that have a description of several operating systems and other info, which looks like this: Windows Server 2008 R2 Member Server Security Technical Implementation Guide; Windows 2008 Member Server Security Technical Implementation Guide; Solaris 10 10 SPARC SECURITY TECHNICAL IMPLEMENTATION GUIDE; and Windows Windows 2003 Member Server Security Technical Implementation Guide.
I need to be able to find and replace (or basically curtail the descriptions) to be Windows 2008 R2; Windows 2008; Windows 2003; and Solaris 10. BUT when I run find and replace with just *2008*, it finds every instance, including the ones with R2 at the end. I need it to only change the ones with 2008 to Windows 2008 and the ones that have 2008 R2 to Windows 2008 R2. I know it is possible, but I have no clue on how to write a macro to do this.
Thanks for your help,
Gerard
Wickedly efficient workaround. Excel really is a powerhouse program, all you have to do is dig into it. Ctl ~ exposes the formulas, and Ctl H allows for the multi edit. Brilliant, Chandoo!