MongoDB dataset : pairs not reducing or problem with script - mongodb

Question

I'm new to programming and mongoDB and learning as I go, I'm attempting a mapreduce on a dataset using mongoDB. So far I've converted the csv to json and imported it into a mongoDB using compass.
In compass the data now looks like this :
_id :5bc4e11789f799178470be53
slug :"bitcoin"
symbol :"BTC"
name :"Bitcoin"
date :"2013-04-28"
ranknow :"1"
open :"135.3"
high :"135.98"
low :"132.1"
close :"134.21"
volume :"0"
market :"1500520000"
close_ratio :"0.5438"
spread :"3.88"
I've added each value as indices as follows, is this the right process so I can run a mapreduce against the data ?
db.testmyCrypto.getIndices()
[
{
"v" : 2,
"key" : {
"_id" : 1
},
"name" : "id",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"slug" : 1
},
"name" : "slug_1",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"symbol" : 2
},
"name" : "symbol_2",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"name" : 3
},
"name" : "name_3",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"data" : 4
},
"name" : "data_4",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"ranknow" : 4
},
"name" : "ranknow_4",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"ranknow" : 5
},
"name" : "ranknow_5",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"open" : 6
},
"name" : "open_6",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"high" : 7
},
"name" : "high_7",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"low" : 8
},
"name" : "low_8",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"volume" : 9
},
"name" : "volume_9",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"market" : 10
},
"name" : "market_10",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"close_ratio" : 11
},
"name" : "close_ratio_11",
"ns" : "myCrypto.testmyCrypto"
},
{
"v" : 2,
"key" : {
"spread" : 13
},
"name" : "spread_13",
"ns" : "myCrypto.testmyCrypto"
}
]
I've scraped the above and now im doing the following from the link to the map-reduce. Is this the correct output, someone ?
> db.testmyCrypto.mapReduce(function() { emit( this.slug, this.symbol ); }, function(key, values) { return Array.sum( values ) },
... {
... query: { date:"2013-04-28" },
... out: "Date 04-28"
... }
... )
{
"result" : "Date 04-28",
"timeMillis" : 837,
"counts" : {
"input" : 0,
"emit" : 0,
"reduce" : 0,
"output" : 0
},
"ok" : 1
}
I've added the "key value pairs" but I don't seem to be able to get anything from the data.
> db.testmyCrypto.mapReduce(function() { emit( this.slug, this.symbol, this.name, this.date, this.ranknow, this.open, this.high, this.low, this.close, this.volume, this.market, this.close_ratio, this.spread ); }, function(key, values) { return Array.sum( values ) }, { query: { slug:"bitcoin" }, out: "Date 04-28" } )
{
"result" : "Date 04-28",
"timeMillis" : 816,
"counts" : {
"input" : 0,
"emit" : 0,
"reduce" : 0,
"output" : 0
},
"ok" : 1 }
>

Answer 1

if you trying to sum some values then they need to numeric (when you importing data to mongo try to set type for values)
db.collectionName.mapReduce(
function() {
emit(
this.slug,
this.open
)
},
function(keySlug, valueOpen) {
return Array.sum(valueOpen)
},
{
query: { date:"2013-04-28" },
out: "Date 04-28"
}
)
this query will return you sum of open values for each slug filtered by date.
ps. you can do same thing with aggregation.
if you have any question let me know.