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Frequently Asked Questions

WReach? Is that connected to WRI somehow?

The "WR" in my name has nothing to do with the company that develops Mathematica. It is just a coincidence.

Why do you start all your global variable names with $?

I use dollar signs for ad hoc global variables because I have been bitten too many times by accidentally assigning an own-value to a symbol that I happen to use, for example, in a symbolic equation. So I am in the habit of writing $x instead of x. I stick to that convention even for longer symbols like $initialUrl. Just like the regular symbol convention, Mathematica's predefined global symbols all start with a capital letter after the $. My ad hoc symbols always start with a lower case letter, so there is no conflict.

Why do you put semicolons and commas at the beginning of the line instead of at the end like a normal person?

I don't think of it that way. Rather, I switch from horizontal to vertical layout when a single expression is too long to fit on one line. This has the interesting side-effect of making the important delimiters stand out and line up. I first ran into this practice in the SQL community. SQL "programs" have the unpleasant property that they must be written as a single statement -- even if that statement is a hundred lines long (or more!). Sometimes Mathematica expressions share that property.


Mar
24
revised Why can I not replace a Dataset using a rule?
changed `Replace` to `ReplaceAll`
Mar
9
revised Can a pattern examine all partitions of a sequence?
edited body
Feb
28
revised Adding Trace produces error messages
added 4 characters in body
Feb
24
revised Can someone explain this snippet: (#[#] &)[#[#][#] &]
by request, added the phrase "infix operator for function definition" to serve as a target for searches
Feb
19
revised Context of localised (dynamic) symbols
added a link to a posting about $CellContext (thanks to @Kuba)
Feb
19
revised Context of localised (dynamic) symbols
minor tweaks
Feb
19
revised Context of localised (dynamic) symbols
edited body
Feb
19
revised Context of localised (dynamic) symbols
I added the sections related to dynamic modules and scoping.
Feb
17
revised Windows command line arguments, stdin & stdout
changed `mmascript.m` to evaluate and print all user-supplied arguments
Feb
16
revised Windows command line arguments, stdin & stdout
Added a variation that uses a _cmd_ file.
Feb
15
revised Windows command line arguments, stdin & stdout
added the section about DOSKEY
Feb
2
revised Can I sum or mulitply 2 columns in a list of associations
added 316 characters in body
Jan
29
revised Does RegularExpression support “(?R)”?
added the section on named patterns
Jan
27
revised How to filter a dataset using Select and a parameter
by request, added mention of the prefix and postfix forms of `#[sel]`
Jan
22
revised Get the wrong result using the StringCase function and Shortest option
grammar, dammit! I'm getting old...
Jan
22
revised Get the wrong result using the StringCase function and Shortest option
grammar, spelling (sorry @bel)
Jan
19
revised Select From List of Nested Associations
`MatchQ` should have been `MemberQ`
Jan
19
revised Select From List of Nested Associations
added the section that details the descending and ascending phases
Jan
19
revised Select From List of Nested Associations
Added the section on re-using queries.
Jan
17
revised Can Trace[] output during evaluation (and not only after)?
expanded the discussion about the `TraceScan` argument *fp*