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This page is a how-to guide detailing a practice or process on the English Wikipedia. |
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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}}}:
Positional parameters {{{1}}} etc. work like named parameters:
{{#if:{{{1|}}}
|1st parameter is '''{{{1}}}'''
|1st parameter is ''blank''}}
Note how the pipe symbol (vertical bar) in the link works as is, it's not quite that easy within Wiki tables, see below.
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:
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:
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:
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.
See also
For avoiding blank rows in the case of successive optional rows, see m:Help:Table#Conditional_table_row.
For more information on #if (and other # functions), see:
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The following help topics deal with templates:
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This help topic deals with table design (since most templates use tables, this may be useful):
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And finally:
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