Help:Array

From Eugene Neighbors

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MediaWiki Handbook: Contents, Readers, Editors, Moderators, System admins Template:Edi

{{#if:|Other languages:}} Template:H-langs: {{#if: Help||}}}} Note: The techniques covered in this article depend on features unavailable before MediaWiki 1.6. This pages explains various methods of creating a kind of associative array using templates.

The two main array techniques are using #switch, and using a template for each element. The other methods, explained after these, are probably obsolete.

1 Function #switch
- 1.1 Limitation
2 Arrays with a template for each element
3 Array technique using parameter defaults
4 Array technique using CSS
5 Comparison of the CSS method and the parameter default method
6 Array technique using a small auxiliary template
- 6.1 For
7 See also
8 Links to other help pages
9 Links to other help pages

[edit] Function #switch

The function #switch provides one of the two main array techniques.

{{#switch:3|1=Mon|2=Tue|3=Wed|4=Thu|5=Fri|6=Sat|7=Son|undefined}} gives {{#switch:3|1=Mon|2=Tue|3=Wed|4=Thu|5=Fri|6=Sat|7=Son|undefined}}
{{#switch:5|1=Mon|2=Tue|3=Wed|4=Thu|5=Fri|6=Sat|7=Son|undefined}} gives {{#switch:5|1=Mon|2=Tue|3=Wed|4=Thu|5=Fri|6=Sat|7=Son|undefined}}
{{#switch:0|1=Mon|2=Tue|3=Wed|4=Thu|5=Fri|6=Sat|7=Son|undefined}} gives {{#switch:0|1=Mon|2=Tue|3=Wed|4=Thu|5=Fri|6=Sat|7=Son|undefined}}

Using Template:Short DOW with switch containing "[[:Template:Short DOW with switch]]":

{{Short DOW with switch|3}} gives Template:Short DOW with switch
{{Short DOW with switch|5}} gives Template:Short DOW with switch
{{Short DOW with switch|0}} gives Template:Short DOW with switch

Put "#default=" in front of the default value if it contains "=":

{{#switch:advanced|simple=1+1=2|#default=999+999=1998}} gives {{#switch:advanced|simple=1+1=2|#default=999+999=1998}}

[edit] Limitation

A serious limitation is the {{#if:|{{#if:pre-expand include size maximum|pre-expand include size maximum|w:Wikipedia:Template limits#}}|{{#if:pre-expand include size maximum|pre-expand include size maximum|w:Wikipedia:Template limits}}}} of 2,048,000 bytes on the Wikimedia wikis. Inclusion of a single array element adds the size of the whole array to the pre-expand include size. Single use of each array element adds the square of the number of elements times the size of each element (including the length of the index, and two bytes for the "=" and "|") to the pre-expand include size.

For example, in a list of Wikipedias we can either use a template for the language names in English, Template:Links-core, or one for the local language names, Template:Links-core, not both: for each of the two, calling it for all languages (about 250) gives a pre-expand include size of more than 1,000,000 bytes, although the expanded wikitext containing both names, and more, is about 100,000 bytes. (In this case the problem can be solved by using parser function #language instead of template "n local".)

[edit] Arrays with a template for each element

An array with a template for each element seems primitive compared with using #switch, but an advantage is that this method is much less affected by the {{#if:|{{#if:pre-expand include size maximum|pre-expand include size maximum|w:Wikipedia:Template limits#}}|{{#if:pre-expand include size maximum|pre-expand include size maximum|w:Wikipedia:Template limits}}}} of 2,048,000 bytes.

A 1D array has elements which are templates with names of the form array-name index, a 2D array (matrix) has elements which are templates with names of the form array-name index1 separator index2. The indexes can be any text.

For example, on Meta there is for each Wikipedia language a template for its English name, e.g. Template:Links-core. They are used on List of Wikipedias/sortable and can also be useful on similar lists. They replace Template:Links-core.

There is also an older, small collection of templates with names of the form "Lang_name_-_language referred to_(language used )" (in fact, the pattern is an example of a generalized form of the name pattern, with a text, here a closing parenthesis, after the second index) with codes used for the two languages; the contents of each template is the word for a language, expressed in the same or another language, e.g. Template:Lang name - de (fr) contains "Allemand", which is "German" in French. (See list; for diagonal elements such as Template:Lang name - de (de) there are, in addition, copies such as Template:Lang name - de). See also explanation page.

In the case of a 2D array separator and the possible values of index1 and index2 should be chosen such that there is no ambiguity; no separator is needed if at least one index is of fixed length, or e.g. if the first index consists of letters and the second of digits. The software does not need to parse index1 separator index2, but for convenient human parsing a separator such as a blank space may be preferred in some cases where it is not strictly needed.

Elements of a 1D array can e.g. be referred to inside a template with {{array-name {{{index}}}}} using parameter index, or similarly with a variable. Also a page can successively call each array element using {{array-name index}} with varying index.

In the case of a 2D array, a template may have a row index as parameter and produce a list based on that row of the matrix, or similarly for columns. See e.g. Template:List of Languages.

A disadvantage of having a template for each array element is that it is extremely cumbersome to copy a large array to another project, unless a bot is used; a sysop may also apply export and import, if those features are enabled.

An advantage is that the absence of a data value shows up as a link to a non-existing template, allowing an individual data value to be added easily. Depending on how fast the servers are, adding multiple values may be slower, sometimes much slower, than when fewer templates have to be edited.

[edit] Array technique using parameter defaults

Template:Links-core, based on parameter defaults, contains (without the newlines):

{{{if{{{1|u}}}|Mon}}}
{{{if{{{2|u}}}|Tue}}}
{{{if{{{3|u}}}|Wed}}}
{{{if{{{4|u}}}|Thu}}}
{{{if{{{5|u}}}|Fri}}}
{{{if{{{6|u}}}|Sat}}}
{{{if{{{0|u}}}|Son}}}

{{short DOW par def|ifu=|3=}} gives Template:Short DOW par def

{{short DOW par def|ifu=|6=|3=|5=|3=}} gives Template:Short DOW par def

The results are in the index order according to the template content, not in the order of the parameters in the template call. Multiple occurrences are removed.

[edit] Array technique using CSS

Unlike other methods, this method works only for final display, and only on modern browsers with enabled support for CSS. The result cannot be used in expressions for template names, parameter names, parameter values, page names in links, etc.

Example:

Template:Links-core contains (without the newlines):

<span style="display:non{{{1|e}}}">Mon</span>
<span style="display:non{{{2|e}}}">Tue</span>
<span style="display:non{{{3|e}}}">Wed</span>
<span style="display:non{{{4|e}}}">Thu</span>
<span style="display:non{{{5|e}}}">Fri</span>
<span style="display:non{{{6|e}}}">Sat</span>
<span style="display:non{{{0|e}}}">Sun</span>

<tt>{{short DOW css d|3=}}</tt> gives Template:Short DOW css d
<tt>{{short DOW css d|6=|3=|5=|3=}}</tt> gives Template:Short DOW css d
Without CSS support the result is MonTueWedThuFriSatSun

Again, the results are in the index order according to the template content, not in the order of the parameters in the template call. Multiple occurrences are removed. A variant of this method uses the common.css class hiddenStructure, example:

Template:Links-core contains (without the newlines):

<span class="hiddenStructur{{{1|e}}}">Mon</span>
<span class="hiddenStructur{{{2|e}}}">Tue</span>
<span class="hiddenStructur{{{3|e}}}">Wed</span>
<span class="hiddenStructur{{{4|e}}}">Thu</span>
<span class="hiddenStructur{{{5|e}}}">Fri</span>
<span class="hiddenStructur{{{6|e}}}">Sat</span>
<span class="hiddenStructur{{{0|e}}}">Sun</span>

<tt>{{short DOW css|3=}}</tt> gives Template:Short DOW css
<tt>{{short DOW css|6=|3=|5=|3=}}</tt> gives Template:Short DOW css
Without CSS support the result is MonTueWedThuFriSatSun

[edit] Comparison of the CSS method and the parameter default method

Comparing the CSS method and the parameter default method, we see that each of the lines

<span style="display:non{{{3|e}}}">Wed</span>
<span class="hiddenStructur{{{3|e}}}">Wed</span>
{{{if{{{3|u}}}|Wed}}}

in a template T, called with

{{T|3=}}
{{T|3=}}
{{T|ifu=|3=}}

respectively, give Wed, and the empty string if 3 is left undefined.

Thus the parameter default method has similar functionality, but requires an extra parameter. It has the advantage that the result can be used in expressions for template names, parameter names, parameter values, page names in links, etc.

For comparison, suppose we would use the shorter word "ifu" instead of "HiddenStructure" (note that this would require that class "if" is undefined); then the lines are:

<span style="display:non{{{3|e}}}">Wed</span>
<span class="if{{{3|u}}}">Wed</span>
{{{          if{{{3|u}}}| Wed}}}

In the third method the wikitext in the template is 15 characters shorter than the second method, for each optional item, but each call is 5 characters longer.

In the second method conflicts with other class names have to be avoided, in the third method conflicts with other parameter names. The first method is best in this regard.

[edit] Array technique using a small auxiliary template

Example:

{{array
 |index=index
 |1=Mon
 |2=Tue
 |3=Wed
 |4=Thu
 |5=Fri
 |6=Sat
 |0=Sun
}}

using Template:Links-core, containing {{{{{{index}}}|{{{default|}}}}}}.

In the case of a constant index this can be useful for selection from predetermined options by a small edit. Alternatively index can be an expression depending on a variable, or, if the text is in a template, on a parameter.

Note that if only one template is used, the difference with the method above is that the array data are outside the template: they are provided in the template call.

Example where the text is in another template (with also a default value): Template:Links-core, containing:

{{array
  |index={{{1}}}
  |1=Mon
  |2=Tue
  |3=Wed
  |4=Thu
  |5=Fri
  |6=Sat
  |0=Sun
  |default={{{1}}} is not a valid weekday number.
}}

Examples:

{{Short DOW|3}} gives Template:Short DOW

{{Short DOW|{{CURRENTDOW}}}} gives Template:Short DOW

{{Short DOW|7}} gives Template:Short DOW

Another version of the two templates could use a term other than "index", e.g. the empty string. However, it should be a term that itself is not used as array index:

{{t Short DOW|3}} using Template:Links-core, containing:

{{array
  |{{{1}}}
  |1=Mon
  |2=Tue
  |3=Wed
  |4=Thu
  |5=Fri
  |6=Sat
  |0=Sun
  |default={{{1}}} is not a valid weekday number.
}}

(hence using implicit name "1" instead of "index") gives "Template:T Short DOW". The implicit 1=3 is overwritten by "1=Mon", and {{{Mon}}} would be produced; since it is undefined, the default is produced, with in this case a confusing error message: not the input is incorrect, but the template itself.

See also Template:Links-core, where parameter names consist of "case: ", followed by the index.

[edit] For

Template:Links-core allows not only to produce one array element, like above, but also more.

Examples:

{{for|call=Short DOW|3}} gives "Template:For/aux"

{{for|call=Short DOW|{{CURRENTDOW}}}} gives "Template:For/aux"

{{for|call=Short DOW|7}} gives "Template:For/aux"

{{for|call=Short DOW|sep=-|3|{{CURRENTDOW}}|7}} gives "Template:For/aux"

{{for|call=Short DOW|6|3|5|3}} gives "Template:For/aux"

Compare the array technique using parameter defaults, and (for final display only) that using CSS, both above.

Differences:

Above only one template is used instead of three.
Above the results are in standard index order, here in the order of the parameters in the template call.
Above multiple occurrences are removed.

[edit] See also

w:en:Portal:Middle-earth/Featured article called in w:en:Portal:Middle-earth: array technique based on parameter defaults
Help:Array (older methods)
Template:Links-core: small example of a method to allow info to be added in a central place (this template, a 1D array with page names as index) displaying the array element concerned on each page.
Attribute: array where each index value is an existing pagename, and the array value is defined on that page using the extension SMW. If the array values are also pagenames (not necessarily existing) the array is called a relation. Compare:
- {{#switch:3|1=Mon|2=Tue|3=Wed|4=Thu|5=Fri|6=Sat|7=Sun|undefined}} gives {{#switch:3|1=Mon|2=Tue|3=Wed|4=Thu|5=Fri|6=Sat|7=Sun|undefined}} (see above)
- <ask>weekday number:=3</ask> giving Wednesday [1]