Expand namespace-prefixed string

Substitutes the namespace prefix in the input vector of strings with the corresponding namespaces.

Usage

expand_prefix(x, namespaces = NULL)

Arguments

x

a character vector of potentially namespace-prefixed strings

namespaces

a named vector of namespaces, with namespace prefixes being the names. A "base" namespace with an empty name can be included. If not provided, or if empty, the input vector is returned as is.

Value

a character vector, of the same length as the input vector

Details

Namespace prefixes are expected to be separated by one or more semicolons. Prefixes that cannot be matched to the vector of namespaces will be left as is. For strings that do not have a namespace prefix, the vector of namespaces can contain a base namespace, identified as not having a name, with which these strings will be expanded.

Examples

uris <- c("cc:license", "dc:title")
ns <- c(dc = "http://purl.org/dc/elements/1.1/",
        dcterms = "http://purl.org/dc/terms/",
        dct = "http://purl.org/dc/terms/",
        cc = "http://creativecommons.org/ns#")
# expansion is vectorized
expand_prefix(uris, ns)
#> [1] "http://creativecommons.org/ns#license"
#> [2] "http://purl.org/dc/elements/1.1/title"

# strings with non-matching or no prefix are left as is
uris <- c(uris, "my:title", "title")
expand_prefix(uris, ns)
#> [1] "http://creativecommons.org/ns#license"
#> [2] "http://purl.org/dc/elements/1.1/title"
#> [3] "my:title"                             
#> [4] "title"                                

# NAs in the input list become NA in the output
uris <- c(uris, NA)
expand_prefix(uris, ns)
#> [1] "http://creativecommons.org/ns#license"
#> [2] "http://purl.org/dc/elements/1.1/title"
#> [3] "my:title"                             
#> [4] "title"                                
#> [5] NA                                     

# can include a "base" (unnamed) namespace for expanding unprefixed strings
ns <- c(ns, "//local/")
xuris <- expand_prefix(uris, ns)
xuris
#> [1] "http://creativecommons.org/ns#license"
#> [2] "http://purl.org/dc/elements/1.1/title"
#> [3] "my:title"                             
#> [4] "//local/title"                        
#> [5] NA                                     
xuris[uris == "title"] == paste0("//local/", uris[uris == "title"])
#> [1] TRUE   NA

# different prefixes may expand to the same result
expand_prefix("dcterms:modified", ns) == expand_prefix("dct:modified", ns)
#> [1] TRUE

# or they may result in different expansions
expand_prefix("dc:title", ns) != expand_prefix("dcterms:title", ns)
#> [1] TRUE