Version: Python

Special variables and constants

Deephaven provides special variables and constants to increase ease of access to row indexes and save users time when writing queries.

Special variables

Special variables inside the query language allow access to the row index of a table.

i is a row index, as a primitive int.
ii is a row index, as a primitive long.
k is a Deephaven internal indexing value, as a primitive long.

note

The variables i and ii both represent row numbers. Integers are limited to values up to 2^31-1 (2,147,483,647), while longs can represent values up to 2^63-1. In other words, to avoid precision problems, use the ii variable, unless an int needs to be passed to another function. Using the i variable in a table with more than 2 billion rows will result in an error.

note

k does not correspond to traditional row numbers and should only be used in limited circumstances, such as debugging or advanced query operations.

caution

These variables are unreliable within a ticking table. Inconsistent results occur since previously created row indexes do not automatically update.

Row numbers i and ii are frequently used with the _ and [] operators to retrieve values from prior or future rows in the table. For example, Column_[ii-1] references the value in Column one row before the current row.

Examples

In the following example, a table is created with the row index as an i int, ii long and k long. The meta-data is assessed to see the variable types.

from deephaven import empty_table

result = empty_table(10).update(formulas=["I = i", "II = ii", "K = k"])

meta = result.meta_table

result
meta

In the following example, row indices, i and ii, are used to access the rows before and after the current row in the table by using the _ and [] operators.

caution

Because i and ii are used, this example will not reliably work on dynamic tables.

from deephaven import empty_table

source = empty_table(10).update(formulas=["X = i"])

result = source.update(
    formulas=[
        "A = X_[i-1]",
        "B = X_[i+1]",
        "C = X_[i+2]",
        "D = sqrt(X_[i-1] + X_[i+1])",
    ]
)

source
result

Deephaven global constants

The deephaven.constants module defines the global constants including Deephaven’s special numerical values. Other constants are defined at the individual module level because they are only locally applicable.

Deephaven provides the following global constants:

MAX_BYTE: The maximum value of type byte.
MAX_CHAR: The maximum value of type char.
MAX_DOUBLE: The maximum value of type double.
MAX_FINITE_DOUBLE: The maximum finite value of type double.
MAX_FINITE_FLOAT: The maximum finite value of type float.
MAX_FLOAT: The maximum value of type float.
MAX_INT: The maximum value of type int.
MAX_LONG: The maximum value of type long.
MAX_SHORT: The maximum value of type short.
MIN_BYTE: The minimum value of type byte.
MIN_CHAR: The minimum value of type char.
MIN_DOUBLE: The minimum value of type double.
MIN_FINITE_DOUBLE: The minimum finite value of type double.
MIN_FINITE_FLOAT: The minimum finite value of type float.
MIN_FLOAT: The minimum value of type float.
MIN_INT: The minimum value of type int.
MIN_LONG: The minimum value of type long.
MIN_POS_DOUBLE: The minimum positive value of type double.
MIN_POS_FLOAT: The minimum positive value of type float.
MIN_SHORT: The minimum value of type short.
NAN_DOUBLE: Not-a-number (NaN) value of type double.
NAN_FLOAT: Not-a-number (NaN) value of type float.
NEG_INFINITY_DOUBLE: Negative infinity value of type double.
NEG_INFINITY_FLOAT: Negative infinity value of type float.
NULL_BOOLEAN: Null value of type bool.
NULL_BYTE: Null value of type byte.
NULL_CHAR: Null value of type char.
NULL_DOUBLE: Null value of type double.
NULL_FLOAT: Null value of type float.
NULL_INT: Null value of type int.
NULL_LONG: Null value of type long.
NULL_SHORT: Null value of type short.
POS_INFINITY_DOUBLE: Positive infinity value of type double.
POS_INFINITY_FLOAT: Positive infinity value of type float.