Loop through object and map to value in JavaScript

Question

I am trying to loop through an object literal and map the substring to a value and plug it into an equation. Right now my code doesn't return an integer but instead is undefined. Here is the code:

function calcFunc(sequence) {
    var dH = 0;
    var dS = 108;
    var i;
    // Compute dH and dS
    for ( i = 0 ; i < ( sequence.length - 1 ) ; i++ ) {
        var pair = sequence.substr(i, 2);
        dH += nn_h[pair];
        dS += nn_s[pair];
    }
    dH *= -100.0;
    dS *= -0.1;
    return dH / ( dS + 1.987 * Math.log( 100 / 4000000000.0 ) ) - 273.15 +
    16.6 * ( Math.log( 50 / 1000.0 ) / Math.log(10) );   
}

example function call would be as follows: var sequence = "tctgtt"; calcFunc(sequence) — Haloor
– Haloor, Commented Nov 4, 2015 at 9:51
Without knowing what your sequence looks like, could it be that you should increase i by 2 in your loop? — icke
– icke, Commented Nov 4, 2015 at 9:52

Richard Dalton · Accepted Answer · 2015-11-04 09:59:28Z

1

Looks like there are at least two errors:

Trying to call log(10) instead of Math.log(10). This is likely causing the undefined error.

Not converting the strings to integers when you load them from the nn_s and nn_h objects. This means you will concatenate the strings rather than add them together as integers.

function calcFunc(sequence) {
    var dH = 0;
    var dS = 108;
    var i;

    // Compute dH and dS
    for ( i = 0 ; i < ( sequence.length - 1 ) ; i++ ) {
        var pair = sequence.substr(i, 2);
        dH += parseInt(nn_h[pair], 10); // parseInt
        dS += parseInt(nn_s[pair], 10); // parseInt
    }

    dH *= -100.0;
    dS *= -0.1;

    return dH / ( dS + 1.987 * Math.log( 100 / 4000000000.0 ) ) - 273.15 +
        16.6 * ( Math.log( 50 / 1000.0 ) / Math.log(10) );   // Math.log(10)
}

Working Fiddle

edited Nov 4, 2015 at 9:59

answered Nov 4, 2015 at 9:56

Richard Dalton

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2 Comments

Jamiec Over a year ago

Im fairly sure the third problem is not increasing the i by 2. Otherwise for the input specified (tctgtt) there is a value for tc but not one for ct

Richard Dalton Over a year ago

@Jamiec Possibly, that depends on the possible sequence values.

Nina Scholz · Accepted Answer · 2015-11-04 10:09:59Z

As I stated:

Math.log() is missing
Values are not numbers
Increment should be 2
Some keys and values are missing (here filled with 0)

The missing values can be replaced by a default value like

dH += nn_h[pair] || 0;
dS += nn_s[pair] || 0;

var nn_s = {
    tc: 135,
    tg: 129,
    tt: 240,
    tn: 168,
    na: 168,
    nc: 210,
    ng: 220,
    nt: 215,
    nn: 203
};
var nn_h = {
    tc: 0,
    tg: 0,
    tt: 0,
    tn: 66,
    na: 66,
    nc: 85,
    ng: 91,
    nt: 80,
    nn: 80
};
function calcFunc(sequence) {
    var dH = 0;
    var dS = 108;
    var i;
    // Compute dH and dS
    for (i = 0 ; i < sequence.length ; i+=2) {
        var pair = sequence.substr(i, 2);
        dH += nn_h[pair];
        dS += nn_s[pair];
    }
    dH *= -100.0;
    dS *= -0.1;
    return dH / (dS + 1.987 * Math.log(100 / 4000000000.0)) - 273.15 +
    16.6 * (Math.log(50 / 1000.0) / Math.log(10));
}

document.write(calcFunc('tctgtt'));

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