拆分字符串数组后未定义（JavaScript）

Question

I wish to split an array of strings ( objData ) into individual elements and copy these to the first row of a 2D array ( sequence ). Please see the code below.

for(i = 0; i < objData.length; i++)
{
    console.log("objData[i]: " + objData[i]);
    parts = objData[i].split(' ');
    sequence[0][n] = parts[1];
    console.log("sequence[0][n]: " + sequence[0][n]);
    sequence[0][n+1] = parts[2];
    sequence[0][n+2] = parts[3];
    n+=3;
    parts = [];
}

Note n is initialised as 0. Each element of objData is a string in the form shown below:

objData[0] = "v 2.11733 0.0204144 1.0852"

I wish to split these strings (from every element of objData ) by using the whitespace as the separator and copy the decimal values to the first row of sequence . I also want to parse these string values to floating point.

Using the code above the values are being copied however the contents of the first row of sequence looks like:

[2.11733NaN, 0.0204144NaN, 1.0852NaN, 2.12303undefined, 0.0131256undefined ..... etc.]

The remaining elements all have 'undefined' appended to them as shown.

I tried using the following line to parse to floating point:

parts = objData[i].split(' ').map(parseFloat);

However the contents of sequence were then:

    [2.11733, 0.0204144, 1.0852, NaN, NaN ..... etc.]

If someone could tell me how to split and parse this data that would be much appreciated! Thank you.

Answer 1

It seems to me that you are making heavy work of this.

Lets take this step by step:

// Make sure sequence array is empty
sequence = [];

// We want to process each element of the objData array :
objData.forEach (function (obj_n) {
  // First split the element, one or more spaces separate fields
  obj_n = obj_n.split (/ +/); // obj_n is now an array
  // Extract elements 1 to 3
  obj_n = obj_n.slice (1, 4); // obj_n is now the three data values
  // Append the three elements to the sequence array:
  sequence = sequence.concat (obj_n);
});

// Now convert to numbers:
sequence = sequence.map (function (f) { return +f });

More compactly :

sequence = [];
objData.forEach (function (obj_n) {
  sequence = sequence.concat (obj_n.split (/ +/).slice (1, 4));
});
sequence = sequence.map (function (f) { return +f });

Answering additional constraints in op comments below

function parseObjData (objData, m, n) { // Add n items to sequence m
  if (!sequence[m]) // make sure sequence[m] exists
    sequence[m] = [];

  objData.forEach (function (obj_n) {
    sequence[m] = sequence[m].concat (obj_n.split (/ +/).
                              slice (1, n + 1));
  });
  sequence[m] = sequence[m].map (function (f) { return +f });
}