Removing characters from a string

Hi,

So I've got an array called questions_raw

questions raw = [
["<Q1> Question",
"choice1","choice2", "choice3"],
["<Q2> Question",
"choice1","choice2", "choice3"],
...
]

And I want to list all of the questions, but not the choices/answers. So far, I've managed to list just the questions, but because another function randomly sorts them, I need to sort them back into numerical order for a separate function (displaying the questions)

I use characters (>,^) at the front to separate them into different answer types (just to explain the code)

I try this to cut each string down so that they can be sorted numerically/alphebetically -

function linearlist()
{
var list = [];
var tempStr = "";
for (var l = 0; l < 145; l++)
{
tempStr = questions_raw[l][0];
list[l] = tempStr;
}

if (list.charAt(0)== " " ) list = list.substring(3);
if (list.charAt(0)== ">" ) list = list.substring(3);
if (list.charAt(0)== "^" ) list = list.substring(3);
var sorted = list.sort();

document.Qtext2form.Qtext2.value = sorted.join("\n");
}

But it doesn't like it - because "it has no method charAt"

Any idea what i'm missing? Is it just that you have to put the [l] in every time you call a variable?

Cheers

yes list is an array which has no charAt (which is performed on a string)
list[l] is a string, on which you can perform a charAt
so just shove in [l] or whatever to specify the string inside the array

to put it another way list is say 5 strings
charAt on an array means nothing, an array has no such function
but the second item in the array say is a string
so list[2].charAt(1) means something, charAt is a function you can do on a string

but if you do add in [l] put it inside the loop so l means something


for (var l = 0; l < 145; l++) {
tempStr = questions_raw[l][0];
list[l] = tempStr;
if (list[l].charAt(0)== " " ) list[l] = list[l].substring(3);
if (list[l].charAt(0)== ">" ) list[l] = list[l].substring(3);
if (list[l].charAt(0)== "^" ) list[l] = list[l].substring(3);
}
var sorted = list.sort();

Ahh nice one, that worked. Had to bypass the 'tempStr' bit too. Cheers mate

One thing though, at the moment it puts 11 before 2 (etc). I'll need to sort that out. Apart from that its spot on

you need to change your sort code like this


IV=function(x){if(typeof(x)==='number'){return Math.floor(x);}var v,as,d=0,neg=1;x='e'+x;while(true){v=d;x=x.substring(1)+'e';as=x.charCodeAt(0);d=((as>47)&&(as<58))?((v+(as-48))*10):0;if(d===0){if(as===45){neg=-1;}else{return((neg*v)/10);}}}};

list.sort(function(a, b) {return (IV(a)<IV(b));});



but change IV(a) into IV(a.substring(0,2)) or whatever for the section of string that contains the number

Doesn't really work. This is what i've put in

IV=function(x){if(typeof(x)==='number'){return Math.floor(x);}var v,as,d=0,neg=1;x='e'+x;while(true){v=d;x=x.substring(1)+'e';as=x.charCodeAt(0);d=((as>47)&&(as<58))?((v+(as-48))*10):0;if(d===0){if(as===45){neg=-1;}else{return((neg*v)/10);}}}};
var sorted = list.sort(function(a, b) {return (IV(a.substring(0,1))<IV(b));});
document.Qtext2form.BoxB.value = sorted.join("\n");

(No numbers exceed 2 digits)

They just come up in a random order (15,8,3...) which is what the script seems to do when the sort function isn't working.

you need to change your sort code like this


IV=function(x){if(typeof(x)==='number'){return Math.floor(x);}var v,as,d=0,neg=1;x='e'+x;while(true){v=d;x=x.substring(1)+'e';as=x.charCodeAt(0);d=((as>47)&&(as<58))?((v+(as-48))*10):0;if(d===0){if(as===45){neg=-1;}else{return((neg*v)/10);}}}};

list.sort(function(a, b) {return (IV(a)<IV(b));});




I don't much appreciate giving out this sort of cryptic code — beginners will just copy-paste it without gaining any understanding of what it actually does, and, in all honesty, what it does is horrible.

Here's the monstrosity in all its glory:

IV = function (x) {

if (typeof(x) === 'number'){
return Math.floor(x);
}

var v, as, d = 0, neg = 1;

x = 'e' + x;

while (true) {
v = d;
x = x.substring(1) + 'e';
as = x.charCodeAt(0);
d = ((as > 47) && (as < 58)) ? ((v + (as - 48)) * 10) : 0;

if (d === 0) {
if (as === 45) {
neg = -1;
}
else {
return ((neg * v) / 10);
}
}
}
};

list.sort(function(a, b) {return (IV(a) < IV(b));});


So, what does it do? It sorts strings containing integers in browser dependent (!) order by means of — brace yourself — extracting single digits, getting to their values by comparing them to an ASCII table, and reassembling them to an actual integer.

All in all, this looks like something I could have built in SpaceChem.

I've heard the suggestions that October 1st, being the farthest possible distance from April 1st, is the perfect day for dishing out a prank or two, since people will least expect it, but let's keep it sane here for a moment: That IV function does the same thing parseInt does, only worse.

So, Thrillseeker, please forget that you have ever seen this. Using a regexp to get to that number in there, your whole code can be as simple as this (assuming that the variable questions_shuffled holds the shuffled version of questions_raw):

var extractNumber = function (question) {
return parseInt(question[0].match(/\d+/)[0]);
};

questions_shuffled.sort(function (a, b) {
return extractNumber(a) - extractNumber(b);
});



I wrote before that nomanic's code sorts the array in descending order, but since function(a, b) {return (IV(a)<IV(b));} isn't a consistent comparison function, the resulting order is actually browser dependent.

Thanks for clearing that up venegal

I've tried the code above, and it throws up an error "Cannot read property '0' of null".

What is 'question'? Do i need to substitute that for one of my variables? And do I need to change the 0's in the first function?

And I want to list all of the questions, but not the choices/answers. So far, I've managed to list just the questions, but because another function randomly sorts them, I need to sort them back into numerical order for a separate function (displaying the questions)

So why not make a *SEPARATE* array of *JUST* the questions *BEFORE* you do the sort. And just hang onto that for when you need the list of questions????

questions raw = [
["<Q1> Question",
"choice1","choice2", "choice3"],
["<Q2> Question",
"choice1","choice2", "choice3"],
...
]
var questionsOnly = [];
for ( var r = 0; r < raw.length; ++r )
{
questionsOnly.push( raw[r][0] );
}

*HAS* to be MUCH LESS work than any other solution, doesn't it?

Like I said, the snippet I posted assumes that questions_shuffled holds a reference to the shuffled questions array.

Here's a full working example:


// The original questions
var questions = [
["<Q1> Question", "choice1", "choice2", "choice3"],
["<Q2> Question", "choice1", "choice2", "choice3"],
["<Q3> Question", "choice1", "choice2", "choice3"],
["<Q4> Question", "choice1", "choice2", "choice3"],
["<Q5> Question", "choice1", "choice2", "choice3"]
];
alert(questions);


// Shuffle the questions
questions.sort(function () {return Math.random() - 0.5});
alert(questions);


//Sort the questions to their original order
var extractNumber = function (question) {
return parseInt(question[0].match(/\d+/)[0]);
};
questions.sort(function (a, b) {
return extractNumber(a) - extractNumber(b);
});
alert(questions);

So why not make a *SEPARATE* array of *JUST* the questions *BEFORE* you do the sort. And just hang onto that for when you need the list of questions????


That's probably the sanest advice in this thread so far. I just felt the need to rewrite nomanic's snippet, so no one stumbling on this thread having a similar sorting problem gets the idea that that's the way it's done.

I see how it fits in. I'll give it another try + figure out why it didn't work first time.

Old Pedant, that would be a great idea if the questions were fixed (or if there wasn't many of em). But plan is, new ones will be added all the time. And I may well be doing a major shuffle of the order. If the script works, it'll be a much more sustainable option. Sorry for the slow learning, its been extremely helpful though. Cheers guys.

Your response makes no sense.

No matter *HOW* the array of questions is created, *JUST BEFORE YOU SORT IT* out of its original order, run my code. It will *AUTOMATICALLY* give you an array with *just* the questions, in the original order.

You can go get the questions via ESP for all it matters. Just be sure to plunk in that code to create questionsOnly *before* the shuffle.