List and filter the links of a STAC document

Returns the links of a STAC document as a plain list, optionally keeping only those that satisfy one or more filter expressions. Each expression in ... is evaluated against a single link, with the link's fields (rel, href, type, title) available as names, and the expressions are combined with logical AND. With no expressions, every link is returned.

This mirrors the ergonomics of rstac::links(): instead of writing Filter(function(l) l$rel == "child", doc$links), you write list_links(doc, rel == "child").

A link whose fields make an expression error (for example a link that has no title) is treated as not matching, rather than raising an error. Variables from the calling scope may be used in the expressions.

Usage

list_links(x, ...)

Arguments

x: A STAC document (doc_catalog, doc_collection, or doc_item), or a bare list of links.
...: Optional filter expressions evaluated against each link, e.g. rel == "child". Combined with logical AND.

Value

A list of links (each element as stored on the document). The list is empty when nothing matches.

Examples

catalog <- new_catalog("cat", "Catalog", "Example")
catalog <- add_collection(catalog, new_collection("a", "A", "First"))
catalog <- add_collection(catalog, new_collection("b", "B", "Second"))

# All links
list_links(catalog)
#> [[1]]
#> <STAC Link: self>
#>   href: catalog.json
#>   type: application/json
#> 
#> [[2]]
#> <STAC Link: root>
#>   href: catalog.json
#>   type: application/json
#> 
#> [[3]]
#> <STAC Link: child>
#>   href: collections/a/collection.json
#>   type: application/json
#>   title: A
#> 
#> [[4]]
#> <STAC Link: child>
#>   href: collections/b/collection.json
#>   type: application/json
#>   title: B
#> 

# Only the child links
list_links(catalog, rel == "child")
#> [[1]]
#> <STAC Link: child>
#>   href: collections/a/collection.json
#>   type: application/json
#>   title: A
#> 
#> [[2]]
#> <STAC Link: child>
#>   href: collections/b/collection.json
#>   type: application/json
#>   title: B
#> 

# Combine predicates (logical AND)
list_links(catalog, rel == "child", type == "application/json")
#> [[1]]
#> <STAC Link: child>
#>   href: collections/a/collection.json
#>   type: application/json
#>   title: A
#> 
#> [[2]]
#> <STAC Link: child>
#>   href: collections/b/collection.json
#>   type: application/json
#>   title: B
#>