I have an array of arrays in coffe script. How to convert it in easy way to string and then back to array? So i m expecting like this.It's easy to do it in ruby using eval.How to achieve that in a coffe script?
Thanks in advance.
"[[2,3,4],[2,3,4],[4,6,7]]" =>string
and then [[2,3,4],[2,3,4],[4,6,7]] back to an array again
While you could, in theory, use eval in javascript/coffeescript as well, you probably should not. A better solution would probably be to use JSON, for instance:
coffee -e 'console.log JSON.parse(JSON.stringify([[1,2,3],[4,5,6]]));'
which outputs:
[ [ 1, 2, 3 ], [ 4, 5, 6 ] ]
Related
I'm trying to work through a problem at the moment which is currently doing the rounds on the internet. The problem is: Given an array of characters, find the first non repeating character. I had a go at it and solved it but I was curious about how other people solved it so I did some looking around and found this answer:
let characters = ["P","Q","R","S","T","P","R","A","T","B","C","P","P","P","P","P","C","P","P","J"]
var counts: [String: Int] = [:]
for character in characters {
counts[character] = (counts[character] ?? 0) + 1
}
let nonRepeatingCharacters = characters.filter({counts[$0] == 1})
let firstNonRepeatingCharacter = nonRepeatingCharacters.first!
print(firstNonRepeatingCharacter) //"Q"
Source: Finding the first non-repeating character in a String using Swift
What I don't understand about this solution, is why it always returns Q, when there are other elements "S" "A" "B" and "J" that could be put first when the filter is applied to the dictionary. My understanding of dictionaries is that they are unordered, and when you make one they change from run to run. So if I make one:
let dictionary:[String:Int] = ["P": 9, "C": 8, "E": 1]
And then print 'dictionary', the ordering will be different. Given this, can anyone explain why the solution above works and maintains the order in which the dictionary elements were added?
You are not looking correctly at the code. The filter is not applied to a dictionary. It is applied to the array (characters), which has a defined order. The dictionary is used only to store counts.
Given an input of some objects each containing a set of strings, I want to count the number of occurrences of each string for the entire batch, and output the word counts (to a CSV in my case) alongside each string (preferably sorted by frequency). How can I achieve this in spring batch? I can't find any suitable examples. I've tried to implement this using item readers/processors but am getting the output duplicated, I'm assuming because it's chunked? Should I use Tasklets for this?
Spring Batch : Aggregating records and write count seems close to what I want to achieve, but it's not clear to me how this is working.
The input is along the lines of:
[{
"id": 1,
"tags": ["foo", "bar"]
}, {
"id": 2,
"tags": ["foo", "baz"]
}
...]
and the desired output from that would be
foo, 2
bar, 1
baz, 1
I want parse one of field in Json format its like this
"{a:[[1,2,3,4],[1,2,3,4]]}"
In the above field 'a' want to extract first two digits
I tried with List[Int] in scala its not working. Try extract first two digits in each set like this
a1:1
a2:2
"{a:[[1,2,3,4],[1,2,3,4]]}"
This is not valid JSON.
{
"a": [
[1, 2, 3, 4],
[1, 2, 3, 4]
]
}
a needs to be in double-quotes.
Edit: If this is the value of a field in Json, then it is an object with a field "a" that is a List[List[Int]].
I'm new to scala (from python) and I'm trying to create a Json object that has dynamic keys. I would like to use some starting number as the top-level key and then combinations involving that number as second-level keys.
From reading the play-json docs/examples, I've seen how to build these nested structures. While that will work for the top-level keys (there are only 17 of them), this is a combinatorial problem and the power set contains ~130k combinations that would be the second-level keys so it isn't feasible to list that structure out. I also saw the use of a case class for structures, however the parameter name becomes the key in those instances which is not what I'm looking for.
Currently, I'm considering using HashMaps with the MultiMap trait so that I can map multiple combinations to the same original starting number and then second-level keys would be the combinations themselves.
I have python code that does this, but it takes 3-4 days to work through up-to-9-number combinations for all 17 starting numbers. The ideal final format would look something like below.
Perhaps it isn't possible to do in scala given the goal of using immutable structures. I suppose using regex on a string of the output might be an option as well. I'm open to any solutions regarding data structures to hold the info and how to approach the problem. Thanks!
{
"2": {
"(2, 3, 4, 5, 6)": {
"best_permutation": "(2, 4, 3, 5, 6)",
"amount": 26.0
},
"(2, 4, 5, 6)": {
"best_permutation": "(2, 5, 4, 6)",
"amount": 21.0
}
},
"3": {
"(3, 2, 4, 5, 6)": {
"best_permutation": "(3, 4, 2, 5, 6)",
"amount": 26.0
},
"(3, 4, 5, 6)": {
"best_permutation": "(3, 5, 4, 6)",
"amount": 21.0
}
}
}
EDIT:
There is no real data source other than the matrix I'm using as my lookup table. I've posted the links to the lookup table I'm using and the program if it might help, but essentially, I'm generating the content myself within the code.
For a given combination, I have a function that basically takes the first value of the combination (which is to be the starting point) and then uses the tail of that combination to generate a permutation.
After that I prepend the starting location to the front of each permutation and then use sliding(2) to work my way through the permutation looking up the amount which is in a breeze.linalg.DenseMatrix by using the two values to index the matrix I've provided below and summing the amounts gathered by indexing the matrix with the two sliding values (subtracting 1 from each value to account for the 0-based indexing).
At this point, it is just a matter of gathering the information (starting_location, combination, best_permutation and the amount) and constructing the nested HashMap. I'm using scala 2.11.8 if it makes any difference.
MATRIX: see here.
PROGRAM:see here.
I've read and searched about MongoDB's JSON-BSON constructions but I do not understand (could not find either) how to have nested data and how to query it.
What I'd like to learn is, if somebody wants to store array within an array as in:
id: x,
name: y,
other: z,
multipleArray: [
(lab1: A, lab2: B, lab3:C),
(lab1: AB, lab2: BB, lab3:CB)
(lab1: AC, lab2: BC, lab3:CC)
..
..
]
How to store such data and then retrieve some, a specific or all elements of "multipleArray" contents?
Any resource on the subject would also be highly appreciated.
Bryan had some great advice which you should heed.
Also, as Manoj said, what you actually have is an array of objects. The following might help you out a bit...
Lists are just ordered sequences: [1,2,3...] or [2,292,111]
The first element in the last example is 2, the second is 292... lists/arrays are denoted by square brackets [ ]
Objects map keys to values: { name: "Tyler", age: 26, fav_color: "green" }
name maps to "Tyler", age maps to 25, etc... and objects are denoted by braces { }
A document in mongodb is an object. So, like above, they map keys to values. Those values can be strings, numbers, arrays... or other even other (nested) objects)
So, lets take a look at your document. You have an object (document) that has keys id, name, other, and multipleArray. The value multiple array maps to is an array [ ] of Objects { }.
{
id: x,
name: y,
other: z,
multipleArray: [
{lab1: "A", lab2: "B", lab3:"C"},
{lab1: "AB", lab2: "BB", lab3:"CB"},
{lab1: "AC", lab2: "BC", lab3:"CC"}
]
}
MongoDB has this feature called multikeys, it basically takes the value you are querying for and tries to match it against every value in the array.
If you wanted to find the document where multipleArray contained the document {lab1: "A", lab2: "B", lab3: "C"}, you query like this: db.data.find({multipleArray: {lab1: "A", lab2: "B", lab3: "C"}})
I'm assuming x, y, and z are defined already.
There are more subtleties and complexities, but if you want to learn more read the documentation on the mongodb site here or get a book.
Your question is a bit generic and as such is difficult to give a good answer.
When modeling your data to be stored and queried using MongoDB, you should consider how you plan to actually use and query your data. Based on the answer to that, you should be able to come up with a good data structure for storing the data.
It would be good for you to to familiarize yourself with the MongoDB query methods (http://www.mongodb.org/display/DOCS/Querying) so you can understand the many ways to query data in MongoDB.
Whatever language you are using should have a nice library that should abstract away the low level details of storing and querying the data, but its still going to be important to know what query methods MongoDB supports.
In general, MongoDB queries let you "reach into" nested objects in a given document and that also includes arrays as well.