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[CALL] Most common pitfalls for beginners of Wolfram Language

Wolfram Language (WL) is a powerful multi-paradigm programing language. There is a set of common mistakes that repeatedly tend to entrap new users. This is a call to describe such mistakes building a "black-listing" guide for novice coders. Please consider contributing. I suggest following simple rules (with gratitude adapted from a similar effort):

  • One topic per answer

  • Focus on non-advanced uses (it is intended to be useful for beginners and as a question closing reference)

  • Include a self explanatory title in header style (example: "# Basic built-in function syntax"; see syntax guide )

  • Explain the symptoms, the mechanism behind the scenes and all possible causes and solutions you can think of. Be sure to include a beginner's level explanation (and a more advance one too, if you can)

Please, use "Reply" to a specific comment for structured clarity of nested comments.

Table of Contents
POSTED BY: Vitaliy Kaurov
22 Replies
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Mark Bourland
Mark Bourland
Posted 4 years ago

Keyboard combinations and keyboard mistakes. I'm a longtime Mathematica user but am surprised by the recent inadvertent results when trying to add comments to input. The second line below, the red square, is particularly problematic. It appears at the beginning of the input line and will change the properties of what is usually a variable and assignment operator (set). If it occurs with a variable that is subscripted, I have to reboot Mathematica; undo, Clear[], ClearAll[] will not fix whatever that red square does to my subscripted variables. The freeform input symbol shown is easy to search for (orange box with equals sign), but not so with the red box and other mistakes shown....

Wolfram Notebook
POSTED BY: Mark Bourland
Pedro Cabral
Pedro Cabral
Posted 4 years ago
POSTED BY: Pedro Cabral

Don't perform operations on whole arrays by indexing individual elements....

Horrible:
output = ConstantArray[0, Length[data]]; 
For[j = 1, j <= Length[data], j++, output[[j]] = Sin[data[[j]]]];
output

Bad:
Table[Sin[data[[j]]], {j, 1, Length[data]}]

Nice:
Map[Sin, data]

And if the operation is Listable... Best: Sin[data]
POSTED BY: Jon McLoone

If i would get a euro for every time I see horrible/bad approach…
POSTED BY: Sander Huisman

Subscripted variables are a pain...use [i] indexing instead.
POSTED BY: Yaroslav Bulatov

Properties & Relations of constraining a locator

Since the example of constraining a (interactive, or, editable) point or locator to the edge of the unit circle appears over and over again in different yet similar teaching contexts, it can become confusing for the beginner to discern all the coding variations by heart and know which one to use in a given active coding situation. In order to constrain a locator (or point or plot tracker/tracer or alike) key functions can be Locator, LocatorPane, Dynamic, DynamicModule, Manipulate, TrackingFunction, Slider2D, but not all of them at the same time. It depends on what you want and what you start with.

In the end it all boils down to the exploitation of the optional 2nd argument of Dynamic which must be a function (or a list of functions); typically the function is a pure function func[val, expr] processing the "mouse position" (val) and the dynamic expression expr (usually just a single dynamic variable u).

The attached short notebook tries to give a helpful overview of all seven (common) variations for reference and easy comparison.

Also check out the Monday morning quiz testing your beginner's Wolfram L vocabulary!

Attachments:
exampleConstrain...nb
POSTED BY: Raspi Rascal
David Proffer
David Proffer
Posted 9 years ago

Import and "CurrencyTokens"

Perhaps not 'common' but I was bitten by it twice until I made it 'my' default for data import. I assume for some legacy reason the stripping of currency symbols is the default behavior of the Import[] function. Seems an odd default behavior to me and worse the default behavior is not pointed out as boldly as I think it should be in the documentation.

Import[   , "CurrencyTokens" -> None]

Incorrect Import

Correct Import
POSTED BY: David Proffer
POSTED BY: Neil Singer

Case sensitivity and typos

I am far from a novice user, but I make a lot of typing mistakes, so case sensitivity catches me often...especially on properties and names in WDF, etc.

This command gets an error

ResourceData["On the origin of Species"]

This command gets the data

ResourceData["On the Origin of Species"]

This command gets an error...also I find the error message to be somewhat opaque

DateObject[{2016, 8, 4}, "week"]

This command evaluates the object

DateObject[{2016, 8, 4}, "Week"]
POSTED BY: Aeyoss Antelope
POSTED BY: Benjamin Goodman
POSTED BY: Michael Rogers
POSTED BY: Sander Huisman

New in 12.2, ApplyTo x//=f

It's included on the Input Operator Forms webpage.
POSTED BY: Raspi Rascal
POSTED BY: Sander Huisman
POSTED BY: Raspi Rascal

Also added this explicitly. thanks!
POSTED BY: Sander Huisman

For some reason the following code is not working for me: ?5.5?=Missing["UnknownSymbol", "5.5?"] Has the floor function syntax been updated?
POSTED BY: Peter Burbery
Rohit Namjoshi
Rohit Namjoshi
Posted 4 years ago

Not sure how you are entering the left and right floor brackets but that is the problem,

\[LeftFloor]5.5\[RightFloor]
(* 5 *)

To enter from the keyboard esclfesc and escrfesc where esc is escape.
POSTED BY: Rohit Namjoshi

The forum screwed up some of the symbols and replaced them with ?. Now fixed.
POSTED BY: Sander Huisman
POSTED BY: Sander Huisman
POSTED BY: Patrick Scheibe

Basic syntax of built-in functions

  • All built-in functions start from capital letters and are in CamelCase for compound names. Users of many other programming languages might miss this as they are used to different conventions. Examples: Plot, ListPlot, FindSpanningTree, etc.

  • Arguments of a function are inclosed in square brackets. Round parenthesis are used only for ordering of operations. Again, other languages use different conventions. Examples:

    • Cos[Pi] --- is a function with a single argument Pi.
    • BesselJ[1/2, 5] --- is a function with 2 arguments
    • (2-Cos[Pi])Sin[Pi/3] --- round parenthesis are used to order operations
POSTED BY: Marina Shchitova
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