WP:QIF

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Shortcut: WP:QIF WP:IF

ParserFunctions allow for the conditional display of table rows, columns or cells (and really, just about anything else). The method is fairly straightforward, but has some limitations which are worth explaining.

Basic use

The following example shows a basic use for #if:

{{#if:{{{variable_foo|}}}
|foo is set to '''{{{variable_foo}}}'''
|foo is ''blank''}}

Here, {{{variable_foo}}} is checked to see if it is defined with a non-blank value. The table below shows the output from a template call (we'll call the template {{if_example_1}}) with different values for {{{variable_foo}}}:

Template call	Result
{{if_example_1}}	foo is blank
{{if_example_1|variable_foo=}}	foo is blank
{{if_example_1|variable_foo=value}}	foo is set to value

Positional parameters {{{1}}} etc. work like named parameters:

{{#if:{{{1|}}}
|1st parameter is '''{{{1}}}'''
|1st parameter is ''blank''}}

Template call	Result
{{if_example_1/b| |bar}}	Template:If example 1/b
{{if_example_1/b|foo|bar}}	Template:If example 1/b
{{if_example_1/b|[[m:|not empty]]}}	Template:If example 1/b
{{if_example_1/b|bad=idea}}	Template:If example 1/b
{{if_example_1/b|1=ok=yes}}	Template:If example 1/b

Note how the pipe symbol (vertical bar) in the link works as is, it's not quite that easy within Wiki tables, see below. For more examples wrt "=" see ifdef, it doesn't affect #if:, it's a general pitfall for templates with positional parameters.

Hiding rows entirely

It's also possible to hide rows of data within a table, however, there are issues you should be aware of.

Incorrect usage

Unfortunately #if and the MediaWiki table syntax do not work together well. For example, the following is invalid and will not work:

{| class="infobox"
{{#if:{{{variable_foo|}}}
|
|-
! Foo
| {{{variable_foo}}}
}}
|-
! Bar
| {{{variable_bar}}}
|}

The code above is in {{if_example_2}}. The table below demonstrates the effect when it's used:

Template call	Result
{{if_example_2}}	Template:If example 2
{{if_example_2|variable_foo=}}	Template:If example 2
{{if_example_2|variable_foo=|variable_bar=bar}}	Template:If example 2
{{if_example_2|variable_foo=value}}	Template:If example 2
{{if_example_2|variable_foo=value|variable_bar=bar}}	Template:If example 2

The problem is with the usage of the pipe character (|). This character, in template calls, is used to separate parameters and so is invalid.

Correct usage

Plan A

One method of hiding rows in tables (or other structures within tables) utilizes HTML directly. HTML is more complicated than MediaWiki table syntax, but not much more so. In general, there are only a handful of HTML tags you need to be aware of

• <tr> - this tag creates a new row (similar to |- in MediaWiki table syntax)
• <th> - this tag creates a new header cell within a row (similar to ! in MediaWiki table syntax)
• <td> - this tag creates a new cell within a row (similar to | in MediaWiki table syntax)
• <caption> - this tag creates a caption (similar to |+ in MediaWiki table syntax)

Working from the invalid template example above, by switching to HTML we end up with the following code:

{| class="infobox"
{{#if:{{{variable_foo|}}}
|<tr><th>Foo</th><td>{{{variable_foo}}}</td></tr>}}
|-
! Bar
| {{{variable_bar}}}
|}

The code above is in {{if_example_2a}}. As before, the table below demonstrates the effect when it's used:

Template call	Result
{{if_example_2a}}	Template:If example 2a
{{if_example_2a|variable_foo=}}	Template:If example 2a
{{if_example_2a|variable_foo=|variable_bar=bar}}	Template:If example 2a
{{if_example_2a|variable_foo=value}}	Template:If example 2a
{{if_example_2a|variable_foo=value|variable_bar=bar}}	Template:If example 2a

Plan B

As noted above the only problem is the vertical bar or pipe symbol within a template. Often it's good enough to replace problematic characters by numeric references, e.g. "{" by {, "|" by |, and "}" by }. But for Wiki tables a real "|" delimiter is required — using | doesn't work as delimiter.

A simple trick allows to protect the "|" in template parameter values while still arriving as real "|" delimiter in the Wiki table, see Template:! (edit talk links history). Note that "!" (exclamation mark) has no problems with templates, it's the other delimiter used in Wiki tables. Here's the code for plan B:

{| class="infobox"
{{#if:{{{foo|}}}|
{{!}}-
! Foo
{{!}} {{{foo}}}
}}
|-
! Bar
| {{{bar}}}
|}

The code above is in {{if_example_2b}}. As before, the table below demonstrates the effect when it's used:

Template call	Result
{{if_example_2b|baz=nobar}}	Template:If example 2b
{{if_example_2b|foo=|bar=vbar}}	Template:If example 2b
{{if_example_2b|foo=value}}	Template:If example 2b
{{if_example_2b|foo=value|bar=vbar}}	Template:If example 2b

Getting help

If you find yourself unable to get a template to behave how you like, you can try asking on Village pump, placing a request at Requested templates, or contacting one of the editors listed below.

Known bug

Using undefined positional parameters, especially {{{1}}} or {{{2}}} in any colon function including parser functions like #if: fails under certain conditions.

This can be tricky for the parameter default mechanism, because then it affects only substituted colon functions.

See also

For more information on #if (and other # functions), see:

• Meta-Wiki:ParserFunctions

The following help topics deal with templates:

• m:Help:Template
• m:Help:Advanced templates

This help topic deals with table design (since most templates use tables, this may be useful):

• Help:Table

And finally, a sample template which demonstrates usage of {{qif}} is available:

• Template:Infobox Conditionals - a "model" infobox template which demonstrates this method.

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Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .