KNIME Expressions Guide

The value type BOOLEAN is used for logical values, that are either true or false. If handling optional values, i.e., type BOOLEAN | MISSING, Kleene’s three-valued logic will be applied. For more details see section General rules for comparison operators.

BOOLEAN literals are either TRUE or FALSE

The KNIME Expression Language only supports one type of integral numbers (INTEGER) and one type of floating point numbers (FLOAT). For simplicity, different precisions are not supported.

The value type STRING is used for sequences of Unicode characters (text). The values are represented as a sequence of characters enclosed in double quotes "text" or single quotes 'text'.

The value type MISSING is used for missing values. It is used to represent the absence of a value in a cell or row, either because the value was missing in the input data or because the value could not be computed.

To retrieve the value from a column in the current row, two syntax options are available:

Use $["column name"] for any column name, including those with spaces or special characters. The column name reference between the square brackets follows to rules of STRING literals.

For column names consisting solely of letters, numbers, and underscores (without starting with a number), a shorthand syntax $column_name is allowed.

Column names are case-sensitive.

There are also special identifiers to access the

Sometimes it is necessary to access values from other rows in the table to perform calculations. The KNIME Expression Language allows the use of $["column_name", offset] to reference previous or next rows relative to the current one.

The offset is a static number and must not be an expression itself.

Negative offsets point to previous rows, positive offsets to rows next the current row. Replacing a column will only take effect after evaluating the expression for the whole table. This means that the expression only uses the original data from that column.

Flow variables are accessed using syntax similar to row access, but with two dollar signs:

Use $$["flow var name"] for any flow variable name.

For flow variable names consisting only of letters, numbers, and underscores (without starting with a number), a shorthand syntax $$flow_var_name is permitted as for column names.

Flow variable names are case-sensitive.

Text following a # symbol is considered a comment and is ignored by the interpreter. Comments can be used to annotate code for clarity. Comments can be placed on a separate line or at the end of a line of code.

The following table lists the arithmetic operators available in the KNIME Expression Language, along with their descriptions and typing notes. Arithmetic operations apply also to optional types. If one or both of the operands is missing, the result is missing. For clarity, we omit the optional type in the following table.

If both operands are of the same type, the result is of the same type if not specified otherwise for the specific operator. If one or both of the operand types is optional, the result is optional. If the operands are of type INTEGER and FLOAT (order irrelevant), the INTEGER value is converted to the closest value of type FLOAT, and the result is of type FLOAT.

Comparison operators are used to compare two numeric values (FLOAT and INTEGER) and yield a BOOLEAN result. There are two kinds of comparison operators: ordering and equality.

Comparison operators compare numeric types, while comparing to MISSING always returns FALSE. Equality operators work on all types as long as both operands are of the same type or MISSING, with the exception that INTEGER and FLOAT can be checked for equality, too.

The logical operators and, or, and not apply to BOOLEAN types as well as to their optional BOOLEAN | MISSING types. and and or are binary operators while not is a unary operator.

If both of the operands are of type BOOLEAN, the result is of type BOOLEAN. If the type of one or both of the operands is optional, i.e., BOOLEAN | MISSING, missing values are interpreted as unknown according to Kleene’s three-valued logic.

The operator + can also be used for string concatenation if at least one of the operands is of type STRING or STRING | MISSING.

The missing coalescing operator ?? is a binary operator that returns the left operand if it is not MISSING, otherwise it returns the right operand. Both operands must have the same type and the result is of the same type. If both operands are MISSING values, the result is MISSING. Even though it will rarely be useful, you can pass MISSING as one of the arguments to ??. However, MISSING ?? MISSING is treated as syntax error.

Operator precedence defines the order in which operations are evaluated in an expression, when it contains more than one operator in series. You can always use parentheses (, ) to enforce a specific order of evaluation. The following table lists the operators in order of precedence, from highest to lowest.

Operations with higher precedence are evaluated before those with lower precedence. Operations with the same precedence level are evaluated from left to right except for ** which is evaluated from right to left. In the following we give some examples to illustrate the precedence of the operators.

Functions evaluated row-wise are always lower-case and calls are made using the function name followed by parentheses containing any arguments:

function_name(arg1, arg2, …​)

Each function has a specific number of arguments and types that it expects. If the arguments do not match the expected types, a type error is raised. The return type of a function is determined by the function itself and is not necessarily the same as the input types.

If there are multiple arguments, they must be separated by commas. Each argument can be any valid expression. You may optionally include a trailing comma after the last argument.

Examples:

Aggregation Functions are a special set of functions prefixed with COLUMN_ that calculate aggregations over whole columns, such as their minimum, maximum, or mean values, for example, COLUMN_MIN("Column Name") .

In aggregation functions we offer to provide arguments positionally and by name of the argument. Positional arguments are always first, followed by named arguments. Named arguments are always provided as arg_name=value.

Let’s illustrate that for the aggregation function COLUMN_AVERAGE(column, ignore_nan)