temp by month pt 3. Use of JavaScript arrays

temp-by-month-3.md

temp by month pt 3. Use of JavaScript arrays

Section Goal

Read in data and create an array of cities.

Learning Objectives

• review JavaScript named functions
• review JavaScript arrays
• use of for ... in syntax for JavaScript object
• Use of arrayName.push( information ) for JavaScript arrays
• use of arrayName.shift() to delete first element of array

Steps

1. Create named function called getCities Get cities receives data

   Example:

   function getCities(data) {
   }
   

2. call function from within d3.csv promise function

    d3.csv("city-month.csv").then(function(dataInFunction){
      var cities = getCities(dataInFunction);
   

3. test output with console.log from inside of function

4. assign variable to first line of data

    var firstLine = data[0];
   

5. create empty array below var firstline, create a new variable called arrayOfCities and assign it to an empty array.

6. loop through JavaScript object elements

    for (var key in firstLine) {
        console.log(key);
    }
   

   

   You now have a list of cities. You need to add them to an array so that you can use the cities in the rest of your program.

7. add element to end of array with arrayName.push

   The array is currently empty. []

   Use arrayOfCities.push(key) to add the key to the end of the array.

8. look at array contents

   put the array to console.log after the for loop

9. notice that first element is month and not name of city

10. delete first element using array.shift()

     arrayOfCities.shift();
    

11. return arrayOfCities

12. In the promise function, call getCities and assign the result to the variable cities

---

Full program

  d3.csv("city-month.csv").then(function(dataInFunction){
      var cities = getCities(dataInFunction);
      // console.log(cities);
  });

  function getCities(data) {
      // only use the first object
      var firstLine = data[0];

      // create an empty array to hold the names of cities
      var arrayOfCities = [];

      // loop through object
      for (var key in firstLine) {
          console.log(key);
          arrayOfCities.push(key);
      }

      // delete first element as the first
      // element is the month

      arrayOfCities.shift();

      return (arrayOfCities);
  }