on https://parse.com/docs/js_guide#queries-arrays there is an example how to find objects where the key's array value contains each of the elements 2, 3, and 4 with the following:
// Find objects where the array in arrayKey contains all of the elements 2, 3, and 4.
query.containsAll("arrayKey", [2, 3, 4]);
However, I would like to find objects where the key's array value contains at least one (not necessarily all) of the elements 2,3, and 4.
Is that possible?
I'm not positive, but what happens if you try containedIn?
I think if you pass an array, it checks to see if any are contained.
query.containedIn("arrayKey", [2,3,4]);
I know that if you use equalTo with an array key and a singular value, it checks if the value is in the array and returns TRUE. I think this will do something similar and should work. I think it will check if any value in "arrayKey" is in the passed array. If any key object does, it will return the object.
swift 3.0
let Query:PFQuery = PFQuery(className: “className”)
Query.whereKey(“Field Name”, containedIn: array)// [“1”,”2”,”3”];
Related
I have a Hash
person_params = {"firstname"=>"",
"lastname"=>"tom123",
"addresses_attributes"=>
{"0"=>
{"address_type"=>"main",
"catalog_delivery"=>"0",
"street"=>"tomstr",
"city"=>"tomcity"
}
}
}
With person_params[:addresses_attributes], I get:
# => {"0"=>{"address_type"=>"main", "catalog_delivery"=>"0", "street"=>"tomstr", "zip"=>"", "lockbox"=>"", "city"=>"tomcity", "country"=>""}}
1) How can I get a new hash without the leading 0?
desired_hash = {"address_type"=>"main", "catalog_delivery"=>"0", "street"=>"tomstr", "zip"=>"", "lockbox"=>"", "city"=>"tomcity", "country"=>""}
2) How can I check whether the attributes in the new hash are empty?
Answer 1:
person_params[:addresses_attributes]['0']
Answer 2:
hash = person_params[:addresses_attributes]['0']
hash.empty?
This looks just like a params hash from Rails =D. Anyway, it seems that your addresses_attributes contains some nested attributes. This means that what you have in practice is more of an array of hashes than a single hash, and that's what you see right? Instead of it being an actually Ruby Array, it is a hash with the index as a string.
So how do you get the address attributes? Well if you only want to get the first address, here are some ways to do that:
person_params[:addresses_attributes].values.first
# OR
person_params[:addresses_attributes]["0"]
In the first case, we will just take the values from the addreses_attributes hash, which gives us an Array from which we can take the first item. If there are no values in addresses_attributes, then we will get nil.
In the second case, we will just ask for the hash value with the key "0". If there are no values in addresses_attributes, we will get nil with this method also. (You might want to avoid using the second case, if you are not confident that the addresses_attributes hash will always be indexed from "0" and incremented by "1")
I am trying to set the bird group as two numbers so that when I assign a variable I can use multiple "else if" statements with that one group later on
Code:
Xcode doesn't let me do this I'm in Swift
Let birdgroup: UInt32 = 2, 3
You can use Array, Set, or a tuple to store multiple values in a single variable. If order matters, go with Array or tuple, but if the order doesn't matter, you can use Set. Array and Set both allow you to vary the number of values stored in your variable, while a tuple variable must always be the same length. Also, you can loop over the items in an array or set, but not over a tuple.
Array is the most often used of the three, so if you aren't sure which to use, it's a good first choice.
In summary, this table shows the possibilities and their properties:
Loopable Unloopable
Ordered Array Tuple
Unordered Set (none)
Finally, all the items in an array or set must be of the same type (or derived from the same type, if the array or set is defined with the base class). This is called homogeneous. A tuple can contain different types, also known as heterogeneous.
Homogeneous Heterogeneous
Ordered Array Tuple
Unordered Set (none)
Collection Types in the Swift documentation describes how to use Array and Set.
Array
Create an array with
var birdgroup: [UInt32] = [2, 3]
birdgroup[0] is equal to 2, and birdgroup[1] is equal to 3. You can also access the items by looping:
for bird in birdgroup {
println("\(bird)")
}
Set
You can declare a set with
var birdgroup: Set<UInt32> = [2, 3]
Because sets have no order (imagine every item is tossed together in a bag), you can't request the "first" or "second" item. Instead, loop over each item of the set:
for bird in birdgroup {
println("\(bird)")
}
Tuple
let birdgroup: (UInt32, UInt32) = (2, 3)
Tuples also retain the order of their items. birdgroup.0 is equal to 2, and birdgroup.1 to 3. You can also give each item of the tuple a name if you prefer that to a number:
let birdgroup: (UInt32, UInt32) = (foo: 2, bar: 3)
birdgroup.foo is 2, and birdgroup.bar is 3.
Additionally, the values in a tuple do not all need to be the same type. You can combine different types, such as
let heterogeneousTuple: (UInt32, String) = (2, "three")
I have a method which returns the number of hotels from a webpage:
hotel_count = self.getHotelsList.values
The output of this method is:
[["hotel_0", "hotel_1", "hotel_2", "hotel_3", "hotel_4", "hotel_5", "hotel_6", "hotel_7", "hotel_8", "hotel_9", "hotel_10", "hotel_11", "hotel_12", "hotel_13", "hotel_14", "hotel_15", "hotel_16", "hotel_17", "hotel_18", "hotel_19", "hotel_20", "hotel_21", "hotel_22", "hotel_23", "hotel_24", "hotel_25", "hotel_26", "hotel_27", "hotel_28", "hotel_29", "hotel_30", "hotel_31", "hotel_32", "hotel_33", "hotel_34", "hotel_35", "hotel_36", "hotel_37", "hotel_38", "hotel_39", "hotel_40"]]
I want to know the length of this array, but if I write
hotel_count = self.getHotelsList.values.length
The length is 1. How can I get a length of 41, which is the one I'm expecting?
Thanks
The array you are showing is nested inside another array. So the outer array is of length 1, the inner array is what you want.
To get it you have to first get the first element of the outer array using [0] or first
testList[0].length
testList.first.length
I am not sure why your getHotelsList method returns a nested array, it doesn't appear to need it.
hotel_count = getHotelsList.values.first.length
You can also do it with [0], but first is faster.
Two notes:
You don't need self at the beginning.
It is a bad habit to use camel case for method names in Ruby. it should better be get_hotels_list.
You could convert that into a single array with flatten:
hotel_count = self.getHotelsList.values.flatten.size
a = Array.new(3,[])
a[1][0] = 5
a => [[5], [5], [5]]
I thought this doesn't make sense!
isn't it should a => [[], [5], []]
or this's sort of Ruby's feature ?
Use this instead:
a = Array.new(3){ [] }
With your code the same object is used for the value of each entry; once you mutate one of the references you see all others change. With the above you instead invoke the block each time a new value is needed, which returns a new array each time.
This is similar in nature to the new user question about why the following does not work as expected:
str.gsub /(<([a-z]+)>/, "-->#{$1}<--"
In the above, string interpolation occurs before the gsub method is ever called, so it cannot use the then-current value of $1 in your string. Similarly, in your question you create an object and pass it to Array.new before Ruby starts creating array slots. Yes, the runtime could call dup on the item by default…but that would be potentially disastrous and slow. Hence you get the block form to determine on your own how to create the initial values.
I have a set of large text files that in total contain about 3 million rows.
What I want to do is pluck a value from a given column from each row and add it to an array in memory. If the value already exists in the array, then ignore it.
I'm assuming the fastest way is NOT:
Read a value
if exists (using array's native index or what-have-you method), then push it to the array
Should I be inserting the value in alphabetical order to speed up the match/search?
OR should I keep multiple arrays...for example, one for each letter of the alphabet?
Use Set:
Set implements a collection of unordered values with no duplicates. This is a hybrid of Array's intuitive inter-operation facilities and Hash's fast lookup.
Example usage:
require 'set'
set = Set.new
set << 1 << 2 << 3 # => #<Set: {1, 2, 3}>
set << 2 # => #<Set: {1, 2, 3}>
You could add the values as keys to a hash map, that would take care of removing duplicates automatically. You could even count the number of times each value occurs this way (with the hash value).