b740c58bf3476bf6bba92359dae0a8f0c85efbe4 kent Tue Aug 13 11:53:16 2019 -0700 Adding doc on 'and' and 'or' operations. Adding details of what happens when you add mixed string to numbers. diff --git src/lib/strex.doc src/lib/strex.doc index 542ab3b..ec07ed4 100644 --- src/lib/strex.doc +++ src/lib/strex.doc @@ -1,75 +1,99 @@ The strex language is a small string expression evaluation language. This document describes its built in functions and operators: -+ - returns the concatenation of the surrounding strings. Will convert a number to a string ++ - returns the concatenation of the surrounding strings or the addition of surrounding + numbers. Will convert a number to a string in mixed expressions + +or - logical or operation extended to strings and numbers. + for logic - if any or-separated-values are true, return true, else false + for numbers - if any or-separated non-zero numbers exist, return first one else 0 + for strings - if any or-separated non-empty strings exists, return first one else "" + In mixed operations result is converted to strings if strings are involved or + the values "" and "true" if no strings are involved. + For the pure string case this can be useful for setting defaults as well. For + instance presuming you might or might not have filled in values for the city or country + variables in the given expression that would return a location of some sort + city or country or "somewhere in the universe" + + +and - logical and operation extended to strings and numbers + for logic - if all and-separated-values are tru, return true, else false + for numbers - if all numbers are non-zero return true else false + for strings - if all and-separated strings are nonempty, return true, else "" + In mixed operations result is converted to strings if strings are involved or + the values "" and "true" if no strings are involved. + +returns first nonempty string or non-zero number on either side of | or "" if all empty +& - returns first empty string or zero on either side of & or right side if all non-empty + [index] - selects a character from string given an integer zero based index. As in Python if index is negative it selects characters from the end of the string. -1 corresponds to the last character of string, as 0 corresponds to first. Returns empty string if index out of range. between(prefix, string, suffix) - returns the part of string found between prefix and suffix example: between("abc", "01234abcHelloxyz56789", "xyz") fetches just "Hello" If there are multiple places the prefix occurs, it will choose the first one, and the then the first place the suffix matches after that. The biologist might think of it as a text oriented PCR, though the primer prefix and suffixes are not included in the output. The prefix "" corresponds to beginning of string and the suffix "" corresponds to end. Returns empty string if nothing found. split(string, index) - white space separated word from string of given 0 based index. Returns empty string if index is too large. A negative input will work much like an array index does, with -1 selecting the last word in the string. Returns empty string if index out of range. separate(string, splitter, index) - separates string with splitter character. Returns string of given index. Index can be negative as in split to pick off of end rather than start. Returns empty string if index is too out of rnge. [start:end] - Use a colon in an array index to select a range of a string. This follows Python conventions, where start is zero based and end is one past the end of this string (or equivalently one based). If start is left out the start of the string is implied. If end is left out the end of the string is emplied. This leads to some curious but useful constructs such as these shown with an example applied to the string "0123456789" [:3] = "012" - first three characters of string [3:] = "3456789" - everything past the first three characters [3:5] = "34" - two characters from the fourth up through the fifth [5:3] = "" - you get an empty string if the start is bigger than the end [3] = "3" - the fourth character (the fun of zero based indexes [-3] = "7" - the third character from the end [-3:] = "789" - last three characters of string [:-3] = "0123456" - everything up to the last three Python actually goes further than this and allows a third, step, specification that strex has not implemented. untsv(string, index) - separate by tab. Synonym for separate(string, '\t', index) uncsv(string, index) - do comma separated value extraction of string. Includes quote escaping. trim(string) - returns copy of string with leading and trailing spaces removed strip(string, toRemove) - remove all occurrences of any character in toRemove from string replace(string, oldPart, newPart) - returns string with all instances of old replaced by new. The cases where either old or new are empty string are useful special cases. If new is "", then all instances of the old string will be deleted. If old is "", then empty strings will be replaced by new strings, useful in setting a default value for a field. fix(string, target, newString) - similar to replace but works at the whole string level. Returns string unchanged except for the case where string matches target exactly. In that case it returns newString instead. The name "fix" comes from it being used generally to replace one constant, fixed, string with another. Also, a lot of the time when you do this it is to fix a small inconsistency in the metadata. In general fix is faster to execute and quicker to type than replace and the effects are more specific. example to help clean up minor variations in vocabulary fix(fix(fix(fix( sex, "M","male"), "F","female"), "Male","male") "Female","female") example to give something a value if non is present fix(requiredField, "", "reasonable default value") md5(string) - returns an MD5 sum digest/hash of string. Useful for creating IDs out of large or merged fields. now() - returns current time and date in a really aweful unix ctime(2) format. We will improve it.