Description

Highly flexible random string generator with no recursion.
Includes options for min/max ANSI code, min/max string length, count of output strings, alpha case. Also permits restricting output to ANSI ranges Alpha, Numeric, Alphanumeric, All printing, All.

Very fast for most tasks. Passable if you want a lot of strings where some may be very short and others very long. Tested 1 million random strings of fixed length 10 with difference character sets, run time about 2 mins. Excel does not crash or barf or run out of memory or bog down the CPU. It just takes its own sweet time.

This could certainly be improved upon in terms of performance. I left it as written for readability and ease of customization. If the built-in flexibility is not sufficient, you can create your own custom category and add it as a defined character set. 1) Add its name to the SWTICH defining the ANSI variable 2) Add its definition to BaseArray. The CHAR(XLOOKUP(RANDARRAY pattern is for non-contiguous ranges (NOTE uses binary lookup and must be sorted ascending), the CHAR(RANDARRAY pattern for contiguous.

Code

\\Inputs -- min and max ANSI code, min and max string length, count of output strings, alpha case, ANSI range 
\\
\\NOTE no parameter is optional but all have default values, so the formula may be written   
\\=Random_String_Generator(, , , , , , )
\\Alpha case only has effect when alpha characters are in the custom or predefined range selected.  
\\
\\Input boundaries:
\\ANSI code -- 1 - 255
\\string length -- 1 to Excel cell content limit
\\count of output strings -- 1 to Excel worksheet row limit
\\alpha case -- "Both", "Upper", "Lower"
\\ANSI range -- "Alpha", "Numeric", "Alphanumeric", "All printing", "All"

=LET(
    DefaultMinANSI, 1,
    DefaultMaxANSI, 255,
    DefaultMinLength, 3,
    DefaultMaxLength, 100,
    DefaultCountOfStrings, 1,
    DefaultAlphaCase, "Both",
    DefaultANSIRange, "All",
    MinANSI, IF(ISOMITTED(intMinANSI), DefaultMinANSI, intMinANSI),
    MaxANSI, IF(ISOMITTED(intMaxANSI), DefaultMaxANSI, intMaxANSI),
    MinStringLength, IF(ISOMITTED(intMinLength), DefaultMinLength, intMinLength),
    MaxStringLength, IF(ISOMITTED(intMaxLength), DefaultMaxLength, intMaxLength),
    CountOfStrings, IF(ISOMITTED(intCountOfStrings), DefaultCountOfStrings, intCountOfStrings),
    AlphaCase, IF(ISOMITTED(strCaseSelection), DefaultAlphaCase, strCaseSelection),
    ANSIRange, IF(ISOMITTED(strANSIRangeSelection), DefaultANSIRange, strANSIRangeSelection),
    ANSISequence, SEQUENCE(255),
    ASCIICanonicalNonPrinting, SEQUENCE(32),
    ASCIIDigits, SEQUENCE(10, , CODE("0")),
    ASCIIUCaseLetters, SEQUENCE(26, , CODE("A")),
    ASCIILCaseLetters, SEQUENCE(26, , CODE("a")),
    ASCIIDelete, 127,
    ANSINonPrinting, {129; 131; 136; 144; 152},
    ANSINonBreakingSpace, 160,
    comment, "ANSINonAlphanumericPrinting is inferred as 'absent from all enumerated sets'",
    ANSIAlphanumericNonPrinting, HSTACK(
        NOT(ISNA(XMATCH(ANSISequence, ASCIIDigits, 0, 2))),
        NOT(ISNA(XMATCH(ANSISequence, ASCIIUCaseLetters, 0, 2))),
        NOT(ISNA(XMATCH(ANSISequence, ASCIILCaseLetters, 0, 2))),
        NOT(ISNA(XMATCH(ANSISequence, ASCIICanonicalNonPrinting, 0, 2))),
        NOT(ISNA(XMATCH(ANSISequence, ASCIIDelete, 0, 2))),
        NOT(ISNA(XMATCH(ANSISequence, ANSINonPrinting, 0, 2))),
        NOT(ISNA(XMATCH(ANSISequence, ANSINonBreakingSpace, 0, 2)))
    ),
    ANSINonAlphanumericPrintingUnfiltered, SEQUENCE(255) *
        --BYROW(ANSIAlphanumericNonPrinting, LAMBDA(r, ISNA(MATCH(TRUE, r, 0)))),
    ANSINonAlphanumericPrinting, FILTER(
        ANSINonAlphanumericPrintingUnfiltered,
        ANSINonAlphanumericPrintingUnfiltered <> 0
    ),
    ASCIILetters, SWITCH(
        AlphaCase,
        "Both", VSTACK(ASCIIUCaseLetters, ASCIILCaseLetters),
        "Upper", ASCIIUCaseLetters,
        "Lower", ASCIILCaseLetters
    ),
    ANSI, SWITCH(
        ANSIRange,
        "Alpha", ASCIILetters,
        "Numeric", ASCIIDigits,
        "Alphanumeric", VSTACK(ASCIIDigits, ASCIILetters),
        "All printing", SORT(VSTACK(ASCIIDigits, ASCIILetters, ANSINonAlphanumericPrinting)),
        "All", SEQUENCE(MaxANSI, , MinANSI)
    ),
    CountOfANSI, COUNT(ANSI),
    ANSIIndexed, HSTACK(SEQUENCE(CountOfANSI, , 1), ANSI),
    BaseArray, SWITCH(
        TRUE,
        OR(ANSIRange = "All printing", LEFT(ANSIRange, 5) = "Alpha"), CHAR(
            XLOOKUP(
                RANDARRAY(CountOfStrings, MaxStringLength, 1, CountOfANSI, TRUE),
                INDEX(ANSIIndexed, , 1),
                INDEX(ANSIIndexed, , 2),
                " absent",
                0,
                2
            )
        ),
        ANSIRange = "All", CHAR(RANDARRAY(CountOfStrings, MaxStringLength, MinANSI, MaxANSI, TRUE)),
        ANSIRange = "Numeric", CHAR(
            RANDARRAY(CountOfStrings, MaxStringLength, CODE("0"), CODE("9"), TRUE)
        )
    ),
    StringLengthArray, RANDARRAY(ROWS(BaseArray), , MinStringLength, MaxStringLength, TRUE),
    BaseArrayConcatenated, BYROW(BaseArray, LAMBDA(r, CONCAT(r))),
    test, XLOOKUP(
        RANDARRAY(CountOfStrings, MaxStringLength, 1, CountOfANSI, TRUE),
        INDEX(ANSIIndexed, , 1),
        INDEX(ANSIIndexed, , 2),
        " absent",
        0,
        2
    ),
    output, LEFT(BaseArrayConcatenated, StringLengthArray),
    output
)