xml_child() function to make selection easier

[jimhester]

With the current implementation you can do the following

x <- read_xml("<x><y/><z><y/></z></x>")

xml_child(x)
#> {xml_node}
#> <y>
xml_child(x, 2)
#> {xml_node}
#> <z>
#> [1] <y/>
xml_child(x, "y")
#> {xml_node}
#> <y>
xml_child(x, "z")
#> {xml_node}
#> <z>
#> [1] <y/>

Some questions before I add docs/tests

• Is this a good function signature or were you thinking of something different?
• Do we also want this same functionality for xml_sibling() and xml_parent()?
• Do we want these functions to be generic with methods for xml_node and xml_nodeset?
• Do we want to modify the existing xml_parent() to use this same signature or keep it as-is?

[hadley]

Needs else that throws error

[hadley]

1. Yes, that looks right to me.
2. I don't think so.
3. I don't think it needs to be since xml_children() is already generic.
4. Leave as is.

[hadley]

"If there are multiple child nodes with the same name, the first will be returned"

[codecov-io]

Current coverage is 58.89%

Merging #94 into master will decrease coverage by 0.69%

@@             master        #94   diff @@
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  Files            30         30          
  Lines          1356       1355     -1   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
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- Hits            808        798    -10   
- Misses          548        557     +9   
  Partials          0          0          

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[jimhester]

@hadley anything else you think needs to change with this or should I merge it?

[hadley]

LGTM