Creates a reusable schema that controls how write_parquet() stores selected
columns. Each argument must be named and may be a type string or a list whose
first element is the type. Schemas may be partial: unspecified columns keep
qio's automatic mapping.
Details
Supported declarations are "AUTO", "BOOLEAN", "INT32", "INT64",
"FLOAT", "DOUBLE", "STRING", "DATE", "TIMESTAMP", "BINARY",
"GEOMETRY", and "GEOGRAPHY".
TIMESTAMP accepts unit ("MILLIS", "MICROS", or "NANOS") and must
be adjusted to UTC. All types accept repetition_type ("AUTO",
"REQUIRED", or "OPTIONAL").
INT32 and INT64 declarations accept finite whole-number inputs; INT64
is limited to R's exact double-integer range from -2^53 through 2^53.
FLOAT and DOUBLE accept numeric input, STRING accepts character or
factor input, DATE accepts Date or whole-number days, and TIMESTAMP
accepts POSIXct.
"BINARY", "GEOMETRY" and "GEOGRAPHY" take a list of raw vectors, with
NULL for a missing value; such a list is written as BINARY without a
schema. GEOMETRY and GEOGRAPHY hold well-known binary (WKB) and accept
crs, a string of at most 127 bytes such as "OGC:CRS84" (the default),
"EPSG:4326", or "projjson:<key>" naming a footer write_parquet()
metadata entry that holds the PROJJSON. GEOGRAPHY also accepts
algorithm, the edge interpolation: "SPHERICAL" (the default),
"VINCENTY", "THOMAS", "ANDOYER", or "KARNEY". qio does not parse the
WKB beyond what geospatial_statistics() records.
Examples
parquet_schema(
id = "INT64",
price = "FLOAT",
created_at = list("TIMESTAMP", unit = "MILLIS")
)
#> <qio_parquet_schema: 3 columns>
#> name physical_type logical_type logical_details
#> 1 id INT64 <NA> <NA>
#> 2 price FLOAT <NA> <NA>
#> 3 created_at INT64 TIMESTAMP unit=MILLIS, adjusted_to_utc=true
#> repetition_type
#> 1 AUTO
#> 2 AUTO
#> 3 AUTO
parquet_schema(
shape = list("GEOMETRY", crs = "EPSG:4326"),
route = list("GEOGRAPHY", algorithm = "KARNEY")
)
#> <qio_parquet_schema: 2 columns>
#> name physical_type logical_type logical_details
#> 1 shape BYTE_ARRAY GEOMETRY crs=EPSG:4326
#> 2 route BYTE_ARRAY GEOGRAPHY crs=OGC:CRS84, algorithm=KARNEY
#> repetition_type
#> 1 AUTO
#> 2 AUTO