String functions - Amazon IoT SiteWise
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String functions

In transforms and metrics, you can use the following functions to operate on strings. For more information, see Using strings in formulas.

Important

Formula expressions can only output double or string values. Nested expressions can output other data types, such as strings, but the formula as a whole must evaluate to a number or string. You can use the jp function to convert a string to a number. The Boolean value must be 1 (true) or 0 (false). For more information, see Undefined, infinite, and overflow values.

Function Description

len(s)

Returns the length of the string s.

find(s, substring)

Returns the index of the string substring in the string s.

contains(s, substring)

Returns 1 if the string s contains the string substring, otherwise 0.

upper(s)

Returns the string s in uppercase form.

lower(s)

Returns the string s in lowercase form.

jp(s, json_path)

Evaluates the string s with the JsonPath expression json_path and returns the result.

Use this function to do the following:

  • Extract a value, array, or object from a serialized JSON structure.

  • Convert a string to a number. For example, the formula jp('111', '$') returns 111 as a number.

To extract a string value from a JSON structure and return it as a number, you must use multiple nested jp functions. The outer jp function extracts the string from the JSON structure, and the inner jp function converts the string to a number.

The string json_path must contain a string literal. This means that json_path can't be an expression that evaluates to a string.

Examples

  • jp('{"status":"active","value":15}', '$.value') returns 15.

  • jp('{"measurement":{"reading":25,"confidence":0.95}}', '$.measurement.reading') returns 25.

  • jp('[2,8,23]', '$[2]') returns 23.

  • jp('{"values":[3,6,7]}', '$.values[1]') returns 6.

  • jp('111', '$') returns 111.

  • jp(jp('{"measurement":{"reading":25,"confidence":"0.95"}}', '$.measurement.confidence'), '$') returns 0.95.

join(s0, s1, s2, s3, ...)

Returns a concatenated string with a delimiter. This function uses the first input string as a delimiter and joins the remaining input strings together. This behaves similar to the join(CharSequence delimiter, CharSequence... elements) function in Java.

Examples

  • join("-", "aa", "bb", "cc") returns aa-bb-cc

format(expression: "format") or format("format", expression)

Returns a string in the specified format. This function evaluates expression to a value, and then returns the value in the specified format. This behaves similar to the format(String format, Object... args) function in Java. For more information about supported formats, see Conversions under Class Formatter in the Java Platform, Standard Edition 7 API Specification.

Examples

  • format(100+1: "d") returns a string, 101.

  • format("The result is %d", 100+1) returns a string, The result is 101.

f'expression'

Returns a concatenated string. With this formatted function, you can use a simple expression to concatenate and format strings. These functions may contain nested expressions. You can use {} (curly braces) to interpolate expressions. This behaves similar to the formatted string literals in Python.

Examples

  • f'abc{1+2: "f"}d' returns abc3.000000d. To evaluate this example expression, do the following:

    1. format(1+2: "f") returns a floating point number, 3.000000.

    2. join('', "abc", 1+2, 'd') returns a string, abc3.000000d.

    You can also write the expression in the following way: join('', "abc", format(1+2: "f"), 'd').