What is a time stamp?
Often when you use excel to track a particular item (like expenses, exercise schedules, investments) you usually enter the current date (and time). This is nothing but timestamping. Once the item is time stamped, it is much more easier to analyze it.
So how do I generate timestamps in Excel?
We all know about the now() formula in excel and how it tells you the current date and time. The only problem with it is that, when you press F9 or recalculate formulas, the now() will be changed to reflect latest date and time. Thus we cannot use NOW() as a time stamp.
A good alternative (although manual) is to use keyboard shortcuts CTRL + ; or CTRL + : to insert current date and time in the active cell. Since this places the value, we don’t need to worry even if the date or time changes. But the only issue is, every time you need a time stamp you have to press the 2 keys.
A better way to get timestamps in excel is to use a special type of formulas, called as circular formulas.
What the heck is a circular formula?
A circular formula refers to itself (or to another cell which in turn refers to this cell). Confused ? Well, let me give you an example.
=if(A2<1000, A2+1,A2)
Now the above formula is normal, but the moment you write it in the cell A2, you have made it a circular formula. So, each time you run the formula (by pressing F9) the value in A2 will go up by 1, just like an incrementing counter.
But here is a thing you should be aware of: There is a setting called “iterations”, it tells excel how many times it should run a formula before finalizing the result.
This setting wouldn’t make any sense in case of regular formulas. But it is very important for circular formulas. If not for this, excel would go in to an infinite loop and stall.
Now, by default iterations in formula computation is turned off. That means when you write a circular formula or create a circular reference, excel shows you a message warning you and it doesn’t evaluate the formula.To turn the iterative calculation, and thus enable usage of circular formulas, go to menu > tools > options > calculation tab and check the iteration box. In excel 2007, you can go to office button > excel options > formulas > iteration area.
As you can see the default max. iterations per formula execution is 100, which means, every time you run the circular formula, excel calculates it 100 times before presenting the value. So our formula =if(A2<1000, A2+1,A2) written in cell A2 would go up by 100 every time you run.
Back to Generating Time Stamps
Now that you are knowledgeable about circular formulas, here is how we can refine the “time stamp generation” problem:
if the cell doesn’t already have time stamp, insert current date time using now(), otherwise leave the value as it is
and we will trigger the formula once we make certain changes, for eg. whenever you enter data, you can tell excel enter timestamps. See this:
The formula itself is very simple:
=IF(C3<>"",IF(B3="",NOW(),B3),"") in cell B3.
What it does?
It checks cell C3 and whenever it is not empty it runs the circular formula IF(B3="",NOW(),B3) which fetches NOW() value only if the cell B3 doesn’t already have a value, thus serving timestamps.
The above formula works only if you have enabled iterative calculation mode as described above.
Your thoughts ?
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12 Responses to “29 Excel Formula Tips for all Occasions [and proof that PHD readers truly rock]”
Some great contributions here.
Gotta love the Friday 13th formula 😀
Great tips from you all! Thanks a lot for sharing! bsamson, particularly you helped me on a terribly annoying task. 🙂
(BTW, Chandoo, it's not exactly "Find if a range is normally distributed" what my suggestion does. It checks if two proportions are statistically different. I probably gave you a bad explanation on twitter, but it'd be probably better if you fix it here... 🙂 )
Great compilation Chandoo
For the "Clean your text before you lookup"
=VLOOKUP(CLEAN(TRIM(E20)),F5:G18,2,0)
I would like to share a method to convert a number-stored-as-text before you lookup:
=VLOOKUP(E20+0,F5:G18,2,0)
@Peder, yeah, I loved that formula
@Aires: Sorry, I misunderstood your formula. Corrected the heading now.
@John.. that is a cool tip.
Hey Chandoo,
That p-value formula is really great for a statistics person like me.
What a p-value essentially is, is the probability that the results obtained from a statistical test aren't valid. So for example, if my p value is .05, there's a 5% probability that my results are wrong.
You can play with this if you install the Data Analysis Toolpak (which will perform some statistical tests for you AND provide the P Value.)
Let's say for example I've got two weeks of data (separated into columns) with the number of hours worked per day. I want to find out if the total number of hours I worked in week two were really all the different than week one.
Week1 Week2
10 11
12 9
9 10
7 8
5 8
Go to Data > Data Analysis > T-Test Assuming Unequal Variances > OK
In the Variable 1 Box, select the range of data for week 1.
In the Variable 2 Box, select the range of data for week 2.
Check "Labels"
In the Alpha box, select a value (in percentage terms) for how tolerant you are of error.
.05 is the general standard; that is to say I am willing to accept a 95% level of confidence that my result is accuarate.
Select a range output.
Excel calculates a number of results: Average (mean) for each week's data, etc.
You'll notice however that there are two P Values; one-tail and two-tail. (one tail tests are for > or .05), the number of hours I worked in week two is statistically equivalent to the number of hours I worked in week one.
So here’s a way you might want to use this. You put up a new entry on your blog. You think it’s the best entry ever! So you pull your webstats for this week and compare it to last week. You gather data for each week on the length of time a visitor spends on your website. The question you’re trying to prove statistically is whether there’s an average increase in the amount of time spent on your website this week as compared to last week (as a result of your fancy new blog post). You can run the same statistical test I illustrated above to find out. Incidentally, it matters very little to the stat test whether the quantity of visitors differs or not.
Anyhow, the Data Analysis toolpack doesn't perform a lot of stat tests that folks like me would like to have access to. In those cases I have to either use different software, or write some very complicated mathematical formulas. Having this p-value formula makes my life a LOT easier!
Thanks!
Eric~
Fantastic stuf..One line explanation is cool.
Thanks to all the contributors
OS
Take FirstName, MI, LastName in access (you can fix it to work in excel) capitalize first letter of each and lowercase the rest and add ". " if MI exists then same for last name:
Full Name: Format(Left([FirstName],1),">") & Format(Right([FirstName]),Len([FirstName])-1),"") & ". ","") & Format(Left([LastName],1),">") & Format(Right([LastName],Len([LastName])-1),"<")
I teach excel, access, etc etc for a living and i have my access students build this formula one step at a time from the inside out to show how formulas can be made even if it looks complicated. Yes I know I could just do IsNull([MI]) and reverse the order in the Iif() function but the point here is to nest as many functions as possible one by one (also I illustrate how it will fail without the Not() as it is)
Extract the month from a date
The easiest formula for this is =MONTH(a1)
It will return a 1 for January, 2 for February etc.
if in a column we write the value of total person for eg. 10 if we spent 1.33 paise each person then how we get total amount in next column and the result will in round form plzzzzz solve my problem sir................... thank u
@Anjali
If the value 10 is in B2 and 1.33 paise is in C2 the formula in D2 could be =B2*C2
If the values are a column of values you can copy the formula down by copy/paste or drag the small black handle at the bottom right corner of cell D2
kindly share with me new forumulas.
How to convert a figure like 870.70 into 870 but 871.70 into 880 using excel formula ? Please help.