rmongodb (version 1.8.0)

mongo.bson.value: Return the value of a mongo.bson field

Description

Search a mongo.bson object for a field by name and retrieve its value.

Usage

mongo.bson.value(b, name)

Arguments

b

A mongo.bson object.

name

(string) The name of a field within b.

Value

• NULL if name is not found; otherwise, the value of the found field.

  This function returns an appropriate R object depending on the type of the field found. This mapping to values is as follows: ll{ mongo.bson.double A double mongo.bson.string A string mongo.bson.object (See below). mongo.bson.array (See below). mongo.bson.binary A raw object. (See below). mongo.bson.undefined A mongo.undefined object mongo.bson.oid A mongo.oid object mongo.bson.bool A logical mongo.bson.date A "POSIXct" class object mongo.bson.null NULL mongo.bson.regex A mongo.regex object mongo.bson.dbref Error! (deprecated -- see link) mongo.bson.code A mongo.code object mongo.bson.symbol A mongo.symbol object mongo.bson.code.w.scope A mongo.code.w.scope object mongo.bson.int An integer mongo.bson.timestamp A mongo.timestamp object mongo.bson.long A double }

  Special handling:

  mongo.bson.object: If the object is recognized as a complex value (of the form { "r" : double, "i" : double }), a complex value is returned. If the special wrapper as output by mongo.bson.buffer.append.object() is detected, an appropriately attributed R object is returned; otherwise, a list is returned containing the subfields.

  mongo.bson.array: If all fields of the array are of the same atomic type, a vector of that type is returned. (Multidimensinal arrays are detected and the dims attribute will be set accordingly. Arrays of complex values are also detected as above). Otherwise, a list is returned containing the subfields.

  mongo.bson.binary: If non-zero, the subtype of the binary data is stored in the attribute "subtype". See mongo.bson.buffer.append.raw().

Details

The search parameter may also be a 'dotted' reference to a field in a subobject or array. See examples.

See Also

mongo.bson.iterator.value, mongo.bson.

Examples

buf <- mongo.bson.buffer.create()
# Append a string
mongo.bson.buffer.append(buf, "name", "Joe")
# Append a date/time
mongo.bson.buffer.append(buf, "created", Sys.time())
# Append a NULL
mongo.bson.buffer.append(buf, "cars", NULL)
b <- mongo.bson.from.buffer(buf)

# Display the date appended above
print(mongo.bson.value(b, "created"))

b <- mongo.bson.from.list(list(name="John", age=32L,
     address=list(street="Vine", city="Denver", state="CO")))
print(mongo.bson.value(b, "age")) # print 32
print(mongo.bson.value(b, "address.state")) # print CO

x <- c(1,1,2,3,5)
b <- mongo.bson.from.list(list(fib=x)) # BSON arrays are 0-based
print(mongo.bson.value(b, "fib.4")) # print 5