Mike Schaeffer's Blog

Thirty days hath September,
the rest I can't remember.
The calendar hangs on the wall;
Why bother me with this at all?

— http://leapyearday.com/30Days.htm

Here's an Excel one liner that computes the number of days in a particular month. Cell A2 contains the year of the month you're looking for, Cell B2 contains the months' ordinal (1=January, 2=February, etc.):

=DAY(DATE(A2,B2+1,1)-1)

This is mainly useful to illustrate what can be done with Excel's internal representation of dates. Dates and times in Windows versions of Excel are normally stored as the number of days from January 1st, 1900. You can see this by entering a date in a cell, and then reformatting the cell to display as a number rather than a date. For example, this reveals April 1st, 2004 to be represented internally as the number 38078. This is because there are 38,078 days between January 1st, 1900 and April 1st, 2004.

The formula above relies on this in its computation of the number of days in a month. The sub-expression DATE(A2,B2+1,1) computes the date number for the first day of the month immediately following the month we're interested in. We then subtract one from that number, which gives us the date number for the last day of the month that we are interested in. The call to DAY then returns the number of the day within the month, which happens to be the number of days in the month.

Michael Sperver has written an SRFI that documents "Octet-Addressed Binary Blocks". Basically these things are like BLOBs in SQL: blocks of memory, opaque to the data model of the language, that can be used to store arbitrary binary data. I can think of a bunch of applications for this:

• An internal representation for compiled byte code functions.
• A way to interoperate with C code that expects binary data formats. (Like the Win32 API, for example. )
• A way to represent binary data longer than a byte that's written to and read from binary ports.

At my job, we use Excel extensively to keep track of software testing progress. One typical use is to maintain a list of features to be tested, along with their current pass/fail statuses and an attempt at a rough subdivision into functional areas. Excel's AutoFilter then makes it easy to ask questions like "show me all failed tests relating to function block scheduling."

This works really well as long as "function block scheduling" is one of the categories into which you've subdivided your features list. If it's not, you have to get a little creative to filter your list. One approach to this problem I've found useful is filtering based on columns populated with a formula similar to this:

=IF(ISERROR(SEARCH($K$5,K6)),"No","Yes")

If column K contains feature descriptions, this formula returns "Yes" is the description matches the search string in K5 and "No", otherwise. Filtering based on this formula makes it possible to display every list item whose description matches a word. If there is more than one column to search, you can use string concatenation to aggregate the columns together:

=IF(ISERROR(SEARCH($K$5,K6&L6&M6)),"No","Yes")

So, why the name apropos? Follow this link.

David Gainer has Summarized a a number of new conditional formatting rules in Excel 12, over on the Excel 12 blog. These rules were designed to "make a greater number of scenarios possible without needing to write formulas." In other words, all these scenarios have simple solutions directly visible in the Excel 12 UI.

Well, if you can't wait for Excel 12, Excel is pretty darned powerful as it is, and as Mr. Gainer states: most of these scenarios have formula-based approaches that work right now. Here are some of the approaches for current versions of Excel:

• With data bars, color scales, or icons based on the numeric value in the cell, percentages, percentiles, or a formula. See the posts on data bars, color scales, and icon sets for more information on each of these. - This approach to 'databars' generalizes to formula-based scaling, although it's not as pretty, not a color scale, and not an icon set.
• Containing, not containing, beginning with, or ending with specific text. For example, highlighting parts containing certain characters in a parts catalog. - Use a formula: a lot of these conditions can be tested using FIND: =FIND(string, A1)=1, checks for parts that begin with string, for example.
• Containing dates that match dynamic conditions like yesterday, today, tomorrow, in the last 7 days, last week, this week, next week, last month, this month, next month. For example, highlight all items dated yesterday. The great part about these conditions is that Excel handles calculating the date based on the system clock, so the user doesn.t need to worry about updating the condition. - Use a formula: the system date is available via NOW(), and Excel offers plenty of date arithmetic functions to check for specific conditions.
• That are blank or that are non-blank. - Use a formula: =ISBLANK(A1) or =NOT(ISBLANK(A1))
• That have errors or that do not have errors. - Use a formula: =ISERROR(A1) or =NOT(ISERROR(A1))
• That are in the top n of a selected range (where n is whatever number you want) OR that are in the top n percent of a selected range (again, where n is adjustable). For example, highlighting the top 10 investment returns in a table of 1,000 investments. - Use a formula: =RANK(A1, range) > n.
• Cells that have the bottom n values OR cells that are the bottom n percent of a selected range. - Use a formula: `=RANK(A1, range)n`.
• Cells that are above average, below average, equal to or above average, equal to or below average, 1 standard deviation above, 1 standard deviation below, 2 standard deviations above, 2 standard deviations below, 3 standard deviations above, 3 standard deviations below a selected range. - This type of thing can be solved using a particular form of formula: =A1<(AVERAGE(ange)-n*STDEV(range)) or =A1>(AVERAGE(ange)+n*STDEV(range)). For large ranges, it probably makes sense to move the computation of AVERAGE and STDEV into a cell, and have the conditional format reference (with an absolute reference) that cell.
• Cells that are duplicate values or, conversely, cells that are unique values. - Use a formula: =COUNTIF(range, A1)=1 or =COUNTIF(range, A1)>1. Ensure that the range you use in the formula has an absolute address. If your range is sorted on the 'key' field, you can use this style of formula: =A1<>A2. This can be much, much faster, particularly for large tables. (For the Comp. Sci. types it's O(N), rather than O(N² ), once you have sorted data.)
• Based on comparisons between two columns in tables. For example, highlight values where values in the .Actual Sales. column are less than in the .Sales Target. column. - Use a conditional format formula: =A1<B1. Apply it to the entire column you want shaded, and Excel will evaluate the seperately for each cell. The cell references in the format formula are relative to the current cell in the selected range. The current cell is the cell in the range that is not highlighted (but is surrounded by a selection border), and can be moved around the four corners of the range with Control+. (period).
• When working with tables, we have also made it easy to format the entire row based on the results of a condition. - Relative formulas can be made to do this: select an entire range, and define a conditional formula using absolute column addresses (ie: =$a1). Excel evaluates the format formula for each cell in the range, and since the column addresses are absolute, each cell in a row will pull from the came columns. Therefore, each cell in a row will share the same conditional format, which is what we want.

Based on this, you don't have to wait for Excel 12 to get a lot of these features, you just have to wait for Excel 12 if you want Excel to do it for you automatically. My suggestion would be to learn how to use conditional formatting formulas, but I tend to be "here's how to fish" kind of guy more than a "here's a fish" kind of guy.