# Selecting functions

The function list displays all available CLEM functions and operators. Scroll to select a function from the list, or, for easier searching, use the drop-down list to display a subset of functions or operators.

The following categories of functions are available:

Function type | Description |
---|---|

Operators | Lists all the operators you can use when building expressions. Operators are also available from the buttons. |

Information | Used to gain insight into field values. For example, the function `is_string`
returns `true` for all records whose type is a string. |

Conversion | Used to construct new fields or convert storage type. For example, the function
`to_timestamp` converts the selected field to a timestamp. |

Comparison | Used to compare field values to each other or to a specified string. For example,
`<=` is used to compare whether the values of two fields are lesser or
equal. |

Logical | Used to perform logical operations, such as `if, then, else`
operations. |

Numeric | Used to perform numeric calculations, such as the natural log of field values. |

Trigonometric | Used to perform trigonometric calculations, such as the arccosine of a specified angle. |

Probability | Returns probabilities that are based on various distributions, such as probability that a value from Student's t distribution is less than a specific value. |

Spatial Functions | Used to perform spatial calculations on geospatial data. |

Bitwise | Used to manipulate integers as bit patterns. |

Random | Used to randomly select items or generate numbers. |

String | Used to perform various operations on strings, such as `stripchar` , which
allows you to remove a specified character. |

Date and time | Used to perform various operations on date, time, and timestamp fields. |

Sequence | Used to gain insight into the record sequence of a data set or perform operations that are based on that sequence. |

Global | Used to access global values that are created by a Set Globals node. For example,
`@MEAN` is used to refer to the mean average of all values for a field across the
entire data set. |

Blanks and Null | Used to access, flag, and frequently fill user-specified blanks or system-missing values. For
example, `@BLANK(FIELD)` is used to raise a true flag for records where blanks are
present. |

Special Fields | Used to denote the specific fields under examination. For example, `@FIELD` is
used when deriving multiple fields. |

After you select a group of functions, double-click to insert the functions into the Expression box at the point indicated by the position of the cursor.

## Database functions

You can run an SPSS Modeler desktop stream file (.str) that contains database functions. But they aren't yet available in the Expression Builder user interface.