deephaven.conversion_utils

Utilities for converting java objects to python object, or vice versa.

NULL_BYTE = -128

Null value for byte.

NULL_CHAR = 65534

Null value for char.

class NULL_CONVERSION

Enum class for specifying desired deephaven -> numpy null conversion behavior.

CONVERT = 2

Pandas style conversion by casting integer type to floating point type, and replacing null values with NaN

ERROR = 0

[default] Raise an exception for integer type (i.e. byte, short, int, or long) primitive null values

PASS = 1

Do not interpret integer type primitive nulls - leave as the reserved constant value

classmethod validateValue(value)

Validates input value for the enum. Returns the default value (i.e. ERROR) if validation fails.

Parameters

value – input value

Returns

best enum version of value

NULL_DOUBLE = -1.7976931348623157e+308

Null value for double.

NULL_FLOAT = -3.4028234663852886e+38

Null value for float.

NULL_INT = -2147483648

Null value for int.

NULL_LONG = -9223372036854775808

Null value for long.

NULL_SHORT = -32768

Null value for short.

convertToJavaArray(input, boxed=False)

Convert the input list/tuple or numpy array to a java array. The main utility of the method is likely providing an object required for a specific java function signature. This is a helper method unifying hung on top of makeJavaArray() and ultimately defined via the proper jpy.array call.

A string will be treated as a character array (i.e. java char array). The user has most control over type in providing a numpy.ndarray, otherwise the contents will be converted to a numpy.ndarray first.

numpy.ndarray Type Conversion:

  • basic numpy primitive dtype are converted to their java analog, NaN values in floating point columns are converted to their respective Deephaven NULL constant values.

  • dtype datatime64[*] are converted to DBDateTime

  • dtype of one of the basic string type *(unicode*, str*, bytes*):

    • if all elements are one character long: converted to char array

    • otherwise, String array

  • ndarrays of dtype numpy.object:

    • ndarrays which are empty or all elements are null are converted to java type Object.

    • Otherwise, the first non-null value is used to determine the type for the column.

    If the first non-null element is an instance of:

    • bool - converted to Boolean array with null values preserved

    • str - converted to String array with null values as empty string

    • datetime.date or datetime.datetime - the array is converted to DBDateTime

    • numpy.ndarray - converted to java array. All elements are assumed null, or ndarray of the same type and compatible shape, or an exception will be raised.

    • dict - unsupported

    • other iterable type - naive conversion to numpy.ndarray is attempted, then as above.

    • any other type:

      • convertUnknownToString=True - attempt to naively convert to String array

      • otherwise, raise exception

  • ndarrays of any other dtype (namely complex*, uint*, void*, or custom dtypes):

    1. convertUnknownToString=True - attempt to convert to column of string type

    2. otherwise, raise exception

Parameters

  • input – string, tuple/list or numpy.ndarray - java type will be inferred

  • boxed – should we ensure that the constructed array is of boxed type?

Returns

a java array instance

convertToJavaArrayList(input)

Convert the input list/tuple or numpy array to a java ArrayList. The main utility of the method is likely providing an object required for a specific java function signature.

Parameters

input – tuple/list or numpy.ndarray - java type will be inferred

Returns

best java.util.ArrayList

Note

The user has most control over type in providing a numpy.ndarray, otherwise the contents will be converted to a numpy.ndarray first. Type mapping will be determined as in convertToJavaArray()

convertToJavaHashMap(input1, input2=None)

Create a java hashmap from provided input of the form (input1=keys, input2=values) or (input1=dict).

Parameters

  • input1 – dict or tuple/list/numpy.ndarray, assumed to be keys

  • input2 – ignored if input1 is a dict, otherwise tuple/list/numpy.ndarray, assumed to be values

Returns

best java.util.HashMap

Note

The user has most control over type in providing keys and values as numpy.ndarray. Otherwise, the keys and values will be converted to a numpy.ndarray first. Type mapping will be determined as in convertToJavaArray()

convertToJavaHashSet(input)

Convert the input list/tuple or numpy array to a java HashSet. The main utility of the method is likely for quick inclusion check inside of a deephaven query.

Parameters

input – tuple/list or numpy.ndarray - java type will be inferred

Returns

best java.util.ArrayList

Note

The user has most control over type in providing a numpy.ndarray, otherwise the contents will be converted to a numpy.ndarray first. Type mapping will be determined as in convertToJavaArray()

convertToJavaList(input)

Convert the input list/tuple or numpy array to a (fixed size) java List. The main utility of the method is likely providing an object required for a specific java function signature.

Parameters

input – tuple/list or numpy.ndarray - java type will be inferred

Returns

best java.util.List

Note

The user has most control over type in providing a numpy.ndarray, otherwise the contents will be converted to a numpy.ndarray first. Type mapping will be determined as in makeJavaArray()

getJavaClassObject(classString)

Gets a java.lang.Class instance corresponding to classString. This is primarily intended as a helper for calling java methods which require setting a type.

Parameters

classString – either a primitive (byte, short, int, long, float, double, char) or a fully qualified java path

Returns

java.lang.Class instance

makeJavaArray(data, name, convertUnknownToString=False)

Utility function which converts a numpy.ndarray to a corresponding java array, where appropriate type is inferred.

numpy.ndarray Type Conversion:

  • basic numpy primitive dtype are converted to their java analog, NaN values in floating point columns are converted to their respective Deephaven NULL constant values.

  • dtype datatime64[*] are converted to DBDateTime

  • dtype of one of the basic string type *(unicode*, str*, bytes*):

    • if all elements are one character long: converted to char array

    • otherwise, String array

  • ndarrays of dtype numpy.object:

    • ndarrays which are empty or all elements are null are converted to java type Object.

    • Otherwise, the first non-null value is used to determine the type for the column.

    If the first non-null element is an instance of:

    • bool - converted to Boolean array with null values preserved

    • str - converted to String array with null values as empty string

    • datetime.date or datetime.datetime - the array is converted to DBDateTime

    • numpy.ndarray - converted to java array. All elements are assumed null, or ndarray of the same type and compatible shape, or an exception will be raised.

    • dict - unsupported

    • other iterable type - naive conversion to numpy.ndarray is attempted, then as above.

    • any other type:

      • convertUnknownToString=True - attempt to naively convert to String array

      • otherwise, raise exception

  • ndarrays of any other dtype (namely complex*, uint*, void*, or custom dtypes):

    1. convertUnknownToString=True - attempt to convert to column of string type

    2. otherwise, raise exception

Parameters

  • data – input numpy.ndarray

  • name – name used to specify source, for logging purposes in case of failure

  • convertUnknownToString – boolean specifying whether to convert unknown types to string

Returns

java array