Is Number Function
DIY is_number Function
Ronald Weidner
I debated about writing this wiki page. It seems like such a simple thing to determine if a string is a number or not. But a lot can go into that question. Euphoria has a function called to_number that you can use to detect whether a string (sequence) is a number or not. For example: https://openeuphoria.org/docs/std_convert.html#_2293_to_number
include std/convert.e sequence some_str = "-0.5" if atom(to_number(some_str, -1)) then atom num = to_number(some_str) end if
If you don't like reinventing the wheel, just use the Euphoria code above to check strings for numbers. But, if you're more like me and want to take a stab at writing a function that can specialize in that functionality... read on.
The to_number function takes 2 arguments. The first is a sequence. The second modifies the output of the function. Sometimes the output is an atom, sometimes a 1-element sequence, and sometimes a 2-element sequence. But honestly, all I really want sometimes is just a true or false... Is this thing a number or not? That's what is_number tries to do. My use case for checking numbers is usually a base-10, signed float or integer. In the future I might write a function named is_number_exp(sequence s, sequence flags) that does more than this function does. It might handle money, percentages, commas, etc. Not because to_number can't already do that, but rather because I like doing those kinds of things.
include std/convert.e include std/sequence.e -- Returns 1 if the string is a valid, undecorated base-10 number (e.g., "42", "-3.14", ".5") -- Returns 0 otherwise. -- -- Notes: -- - No commas, exponents, or hex/octal prefixes allowed. -- - Leading + or - is allowed. -- - A leading or trailing decimal point is valid (e.g., ".5", "5."). -- - Empty strings, multiple dots, or non-digit characters cause failure. function is_number(sequence maybe) integer found_dot = 0 integer i = 1 integer c = 0 integer retval = 0 -- because empty string is not a number if length(maybe) = 0 then return 0 end if -- we'll skip the sign if it has one if find(maybe[i], "+-") then i += 1 end if -- We might have just moved the index. Make sure there is at -- least 1 more character to consider. if i > length(maybe) then return 0 end if -- if nothing follows a leading . maybe isn't a number if equal(maybe[i], '.') and (i + 1 > length(maybe)) then return 0 end if -- At this point i is either 1 or 2. It's 1 if there is no sign. It's -- 2 if there is a sign. maybe[i] might be a . but it might not be. -- If it is a dot at least one more char is required in a valid string. -- Let's say we have this string. "+.." . In that -- case i is 2 when we enter the loop. We'll set retval to 1 and -- consume the first . . The first . is valid. Let's start consuming -- the rest of the string. Anything other than a digit is invalid. -- -- I believe this loop should be able to accurately determine whether or -- not a string is a base-10 undecorated number. Edge cases are already -- dealt with. Looks good on my monitor. while i < (length(maybe) + 1) do c = maybe[i] if equal(c, '.') and found_dot then return 0 end if if equal(c, '.') then found_dot = 1 elsif not find(c, "0123456789") then return 0 end if retval = 1 i+=1 end while return retval end function -- Sequence return will be at least and no more than -- len characters long. if length(s) < len the -- difference will be right padded with spaces. -- If length(s) > len then the return value will be a -- truncated version of s. function fixed_len(sequence s, integer len) if length(s) < len then return s & repeat(' ', len - length(s)) end if return s[1..len] end function sequence false_tests = {" ", ".", "-", "+", "..", ".-", ".+", "-.", "+.", "0..", ".0.", "--", "++", "1 4", "A", "-a", "+a", "-.a", "+.a", ".a", "1a", ".1a ", "7+", "7-", "7Foo", "7*" } sequence true_tests = { "0", "0.", ".0", "-.0", "+.0", "0.0", "-0.0", "+0.0", "123", "123.", ".123", "-.123", "+.123","123.123", "-123.123", "+123.123", "00032", "-00032", "+00032", "00032.000", "-00032.050", "+00032.0", "00000.0000", "-00000.0000" } integer i = 1 puts (1, "Testing for FALSE (0): \n") while i < length(false_tests) + 1 do sequence t = false_tests[i] sequence msg = fixed_len(sprintf("Testing is_number function with input [%s] ",{t} ),55) printf(1, msg & "result: [%d]\n" , {is_number(t)}) i += 1 end while i = 1 puts (1, "Testing for TRUE (1): \n") while i < length(true_tests) + 1 do sequence t = true_tests[i] sequence msg = fixed_len(sprintf("Testing is_number function with input [%s] ",{t} ), 55) printf(1, msg & "result: [%d]\n" , {is_number(t)}) i += 1 end while puts(1,"\n\nWhat would Euphoria do?? atom d = atom(to_number(test_str, -1)) \n\n") i = 1 puts (1, "Testing for FALSE (0): \n") while i < length(false_tests) + 1 do sequence t = false_tests[i] sequence msg = fixed_len(sprintf("What would Euphoria do with input [%s] ",{t} ),55) printf(1, msg & "result: [%d]\n" , {atom(to_number(t, -1))}) i += 1 end while i = 1 puts (1, "Testing for TRUE (1): \n") while i < length(true_tests) + 1 do sequence t = true_tests[i] sequence msg = fixed_len(sprintf("What would Euphoria do with input [%s] ",{t} ),55) printf(1, msg & "result: [%d]\n" , {atom(to_number(t, -1))}) i += 1 end while
$ eui is_number.ex Testing for FALSE (0): Testing is_number function with input [ ] result: [0] Testing is_number function with input [.] result: [0] Testing is_number function with input [-] result: [0] Testing is_number function with input [+] result: [0] Testing is_number function with input [..] result: [0] Testing is_number function with input [.-] result: [0] Testing is_number function with input [.+] result: [0] Testing is_number function with input [-.] result: [0] Testing is_number function with input [+.] result: [0] Testing is_number function with input [0..] result: [0] Testing is_number function with input [.0.] result: [0] Testing is_number function with input [--] result: [0] Testing is_number function with input [++] result: [0] Testing is_number function with input [1 4] result: [0] Testing is_number function with input [A] result: [0] Testing is_number function with input [-a] result: [0] Testing is_number function with input [+a] result: [0] Testing is_number function with input [-.a] result: [0] Testing is_number function with input [+.a] result: [0] Testing is_number function with input [.a] result: [0] Testing is_number function with input [1a] result: [0] Testing is_number function with input [.1a ] result: [0] Testing is_number function with input [7+] result: [0] Testing is_number function with input [7-] result: [0] Testing is_number function with input [7Foo] result: [0] Testing is_number function with input [7*] result: [0] Testing for TRUE (1): Testing is_number function with input [0] result: [1] Testing is_number function with input [0.] result: [1] Testing is_number function with input [.0] result: [1] Testing is_number function with input [-.0] result: [1] Testing is_number function with input [+.0] result: [1] Testing is_number function with input [0.0] result: [1] Testing is_number function with input [-0.0] result: [1] Testing is_number function with input [+0.0] result: [1] Testing is_number function with input [123] result: [1] Testing is_number function with input [123.] result: [1] Testing is_number function with input [.123] result: [1] Testing is_number function with input [-.123] result: [1] Testing is_number function with input [+.123] result: [1] Testing is_number function with input [123.123] result: [1] Testing is_number function with input [-123.123] result: [1] Testing is_number function with input [+123.123] result: [1] Testing is_number function with input [00032] result: [1] Testing is_number function with input [-00032] result: [1] Testing is_number function with input [+00032] result: [1] Testing is_number function with input [00032.000] result: [1] Testing is_number function with input [-00032.050] result: [1] Testing is_number function with input [+00032.0] result: [1] Testing is_number function with input [00000.0000] result: [1] Testing is_number function with input [-00000.0000] result: [1] What would Euphoria do?? atom d = atom(to_number(test_str, -1)) Testing for FALSE (0): What would Euphoria do with input [ ] result: [0] What would Euphoria do with input [.] result: [0] What would Euphoria do with input [-] result: [0] What would Euphoria do with input [+] result: [0] What would Euphoria do with input [..] result: [0] What would Euphoria do with input [.-] result: [0] What would Euphoria do with input [.+] result: [0] What would Euphoria do with input [-.] result: [0] What would Euphoria do with input [+.] result: [0] What would Euphoria do with input [0..] result: [0] What would Euphoria do with input [.0.] result: [0] What would Euphoria do with input [--] result: [0] What would Euphoria do with input [++] result: [0] What would Euphoria do with input [1 4] result: [0] What would Euphoria do with input [A] result: [0] What would Euphoria do with input [-a] result: [0] What would Euphoria do with input [+a] result: [0] What would Euphoria do with input [-.a] result: [0] What would Euphoria do with input [+.a] result: [0] What would Euphoria do with input [.a] result: [0] What would Euphoria do with input [1a] result: [0] What would Euphoria do with input [.1a ] result: [0] What would Euphoria do with input [7+] result: [1] What would Euphoria do with input [7-] result: [1] What would Euphoria do with input [7Foo] result: [0] What would Euphoria do with input [7*] result: [0] Testing for TRUE (1): What would Euphoria do with input [0] result: [1] What would Euphoria do with input [0.] result: [1] What would Euphoria do with input [.0] result: [1] What would Euphoria do with input [-.0] result: [1] What would Euphoria do with input [+.0] result: [1] What would Euphoria do with input [0.0] result: [1] What would Euphoria do with input [-0.0] result: [1] What would Euphoria do with input [+0.0] result: [1] What would Euphoria do with input [123] result: [1] What would Euphoria do with input [123.] result: [1] What would Euphoria do with input [.123] result: [1] What would Euphoria do with input [-.123] result: [1] What would Euphoria do with input [+.123] result: [1] What would Euphoria do with input [123.123] result: [1] What would Euphoria do with input [-123.123] result: [1] What would Euphoria do with input [+123.123] result: [1] What would Euphoria do with input [00032] result: [1] What would Euphoria do with input [-00032] result: [1] What would Euphoria do with input [+00032] result: [1] What would Euphoria do with input [00032.000] result: [1] What would Euphoria do with input [-00032.050] result: [1] What would Euphoria do with input [+00032.0] result: [1] What would Euphoria do with input [00000.0000] result: [1] What would Euphoria do with input [-00000.0000] result: [1]
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