I have a Cars Model in my rails app which has three columns Car_id , car_name and fuel_type. So in my table the car_name is coming many times.
I want to know how can I filter this Car table so that one car_name appears only one time in the returned array?
I want the full filtered table to be returned not just the distinct car names.
Is this what you are looking for?
Car.group(:car_name).all
Maybe you should use this:
cars = Cars.all.uniq {|c| c.car_name}
This will get filtered array of Cars by car_name attribute.
Hopefully this is a little clearer. I'm sorry but I'm very new to coding in general. I have multiple tables that I have to query in succession in order to get to the correct array that I need. The following logic for the query is as follows:
this gives me an array based upon the store :id
store = Stores.find(params[:id])
this gives me another array based upon the param .location found in the table store where that value equals the row ID in the table Departments
department = Departments.find(store.location)
I need to preform one last query but in order to do so I need to figure out which day of the meeting is needed. In order to do this I have to create the parameter day_of_meeting found in the table Stores. I try to call it from the array above and create a new variable. In the Table Departments, I there are params such as day_1, day_2 and so on. I need to be able to call something like department.day_1 or department.day_2. Thus, I'm trying to actually create the variable by join the words "department.day_" to the variable store.day_of_meeting which would equal some integer, creating department.day_1...
which_day = ["department.day_", store.day_of_meeting].join("")
This query finds uses the value found from the variable department.day_1 to query table Meeting to find the values in the corresponding row.
meeting = Meeting.find(which_day)
Does this make my problem any clearer to understand?
findmethod can only accept parameters like Meeting.find(1) or Meeting.find("1-xx").
so, what you need is Meeting.find(department.send("day_" + store.day_of_meeting.to_s))
Hope to help!
I already have a working solution, but I would really like to know why this doesn't work:
ratings = Model.select(:rating).uniq
ratings.each { |r| puts r.rating }
It selects, but don't print unique values, it prints all values, including the duplicates. And it's in the documentation: http://guides.rubyonrails.org/active_record_querying.html#selecting-specific-fields
Model.select(:rating)
The result of this is a collection of Model objects. Not plain ratings. And from uniq's point of view, they are completely different. You can use this:
Model.select(:rating).map(&:rating).uniq
or this (most efficient):
Model.uniq.pluck(:rating)
Rails 5+
Model.distinct.pluck(:rating)
Update
Apparently, as of rails 5.0.0.1, it works only on "top level" queries, like above. Doesn't work on collection proxies ("has_many" relations, for example).
Address.distinct.pluck(:city) # => ['Moscow']
user.addresses.distinct.pluck(:city) # => ['Moscow', 'Moscow', 'Moscow']
In this case, deduplicate after the query
user.addresses.pluck(:city).uniq # => ['Moscow']
If you're going to use Model.select, then you might as well just use DISTINCT, as it will return only the unique values. This is better because it means it returns less rows and should be slightly faster than returning a number of rows and then telling Rails to pick the unique values.
Model.select('DISTINCT rating')
Of course, this is provided your database understands the DISTINCT keyword, and most should.
This works too.
Model.pluck("DISTINCT rating")
If you want to also select extra fields:
Model.select('DISTINCT ON (models.ratings) models.ratings, models.id').map { |m| [m.id, m.ratings] }
Model.uniq.pluck(:rating)
# SELECT DISTINCT "models"."rating" FROM "models"
This has the advantages of not using sql strings and not instantiating models
Model.select(:rating).uniq
This code works as 'DISTINCT' (not as Array#uniq) since rails 3.2
Model.select(:rating).distinct
Another way to collect uniq columns with sql:
Model.group(:rating).pluck(:rating)
If I am going right to way then :
Current query
Model.select(:rating)
is returning array of object and you have written query
Model.select(:rating).uniq
uniq is applied on array of object and each object have unique id. uniq is performing its job correctly because each object in array is uniq.
There are many way to select distinct rating :
Model.select('distinct rating').map(&:rating)
or
Model.select('distinct rating').collect(&:rating)
or
Model.select(:rating).map(&:rating).uniq
or
Model.select(:name).collect(&:rating).uniq
One more thing, first and second query : find distinct data by SQL query.
These queries will considered "london" and "london " same means it will neglect to space, that's why it will select 'london' one time in your query result.
Third and forth query:
find data by SQL query and for distinct data applied ruby uniq mehtod.
these queries will considered "london" and "london " different, that's why it will select 'london' and 'london ' both in your query result.
please prefer to attached image for more understanding and have a look on "Toured / Awaiting RFP".
If anyone is looking for the same with Mongoid, that is
Model.distinct(:rating)
Some answers don't take into account the OP wants a array of values
Other answers don't work well if your Model has thousands of records
That said, I think a good answer is:
Model.uniq.select(:ratings).map(&:ratings)
=> "SELECT DISTINCT ratings FROM `models` "
Because, first you generate a array of Model (with diminished size because of the select), then you extract the only attribute those selected models have (ratings)
You can use the following Gem: active_record_distinct_on
Model.distinct_on(:rating)
Yields the following query:
SELECT DISTINCT ON ( "models"."rating" ) "models".* FROM "models"
In my scenario, I wanted a list of distinct names after ordering them by their creation date, applying offset and limit. Basically a combination of ORDER BY, DISTINCT ON
All you need to do is put DISTINCT ON inside the pluck method, like follow
Model.order("name, created_at DESC").offset(0).limit(10).pluck("DISTINCT ON (name) name")
This would return back an array of distinct names.
Model.pluck("DISTINCT column_name")
in a scenario i want to retrieve the records with different values so i used distinct for that,
Book.where(["user_id = ?",#user_id]).select('distinct title_id')
`this, only retrives the records like this [#<Book title_id: 30>, #<Book title_id: 31> ]`
but i want to fetch the id of Book as well along with title_id
so, please advise me how to work on this
thanks
use grouping:
Book.where(:user_id => #user.id).grouped('title_id')
problem is that if you do grouping you can't have different book ids, they are all grouped into single row. You can use GROUP_CONCAT to workaround that:
Book...select('books.*, GROUP_CONCAT(id) as ids')
that way you'll have book ids attribute for every group
http://about.digg.com/blog/looking-future-cassandra
I've found this article about Digg's move to Cassandra. But I didn't get the author's idea of Bucket for pair (user,item). Little more details on the idea would be helpful to me to understand the solution better.
Thanks
It sounds like they are using one row in a super column family per user with one super column per item; a subcolumn for an item super column represents a friend who dugg the item. At least in pycassa, this makes an insert as simple as:
column_family.insert(user, {item: {friend: ''}})
They could also have done this a couple of other ways, and I'm not sure which they chose.
One is to use a standard column family, use a (user,item) combination for the row key, and use one column per friend who dugg the item:
column_family.insert(user + item, {friend: ''})
Another is to use a standard column family, use just (user) for the row key, and use an (item, friend) combination for the column name:
column_family.insert(user, {item + friend: ''})
Doesn't sound like this is what they used, but it's an acceptable option as well.