Databases
StackOverflow2013
Postsdbo
POMongoDB Map Reduce newbie (PHP)
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POMongoDB Map Reduce newbie (PHP)
    primarykey
    data
    text
    <p>I'm new to the map reduce concept and even though I'm making some slow progress, I'm finding some issues that I need some help with.</p> <p>I have a simple collection consisting of an id, city and and destination, something like this:</p> <pre><code>{ "_id" : "5230e7e00000000000000000", "city" : "Boston", "to" : "Chicago" }, { "_id" : "523fe7e00000000000000000", "city" : "New York", "to" : "Miami" }, { "_id" : "5240e1e00000000000000000", "city" : "Boston", "to" : "Miami" }, { "_id" : "536fe4e00000000000000000", "city" : "Washington D.C.", "to" : "Boston" }, { "_id" : "53ffe7e00000000000000000", "city" : "New York", "to" : "Boston" }, { "_id" : "5740e1e00000000000000000", "city" : "Boston", "to" : "Miami" }, ... </code></pre> <p>(Please do note that this data is just made up for example purposes)</p> <p>I'd like to group by city the destinations including a count:</p> <pre><code>{ "city" : "Boston", values : [{"Chicago",1}, {"Miami",2}] } { "city" : "New York", values : [{"Miami",1}, {"Boston",1}] } { "city" : "Washington D.C.", values : [{"Boston", 1}] } </code></pre> <p>For this I'm starting to playing with this function to map:</p> <pre><code> function() { emit(this.city, this.to); } </code></pre> <p>which performs the expected grouping. My reduce function is this:</p> <pre><code> function(key, values) { var reduced = {"to":[]}; for (var i in values) { var item = values[i]; reduced.to.push(item); } return reduced; } </code></pre> <p>which gives somewhat an expected output:</p> <pre><code>{ "_id" : ObjectId("522f8a9181f01e671a853adb"), "value" : { "to" : [ "Boston", "Miami" ] } } { "_id" : ObjectId("522f933a81f01e671a853ade"), "value" : { "to" : [ "Chicago", "Miami", "Miami" ] } } { "_id" : ObjectId("5231f0ed81f01e671a853ae0"), "value" : "Boston" } </code></pre> <p>As you can see, I still haven't counted the repeated cities, but as can be seen above, for some reason the last result in the output doesn't look good. I'd expected it to be </p> <pre><code>{ "_id" : ObjectId("5231f0ed81f01e671a853ae0"), "value" : { "to" : ["Boston"] } } </code></pre> <p>Has this anything to do with the fact that there is a single item? Is there any way to obtain this?</p> <p>Thank you.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USDan
    1. USDan
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. COIs there a reason that you've picked map reduce over the aggregation frame work to do this(there are valid reasons, but the AF is generally a better choice)?
      singulars
      1. POMongoDB Map Reduce newbie (PHP)
      1. USCharlie Page
    2. CONo other reason than being complete newbie on this. I read that both map reduce and AF would be superior over "Single Purpose Aggregation Operations" so I started with the one most "popular" online.
      singulars
      1. POMongoDB Map Reduce newbie (PHP)
      1. USDan
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload