I am working on an assignment using F# where I have to add in a specific student and his information to a large Students.txt file
The Student.txt file contains their lastname, firstname, middle intial, phone number, email, and their gpa
A snippet of the Students.txt file
If I am trying to add in this information and then read from the file:
type Phone =
type Email =
type StudentInfo =
{ firstName : string;
middleInitial : char option;
lastName : string;
phone : Phone;
email : Email option;
gpa : float }
let addPhone input =
let addEmail input =
let readStudentsFromCSV filename =
let students = readStudentsFromCSV "Students.txt"
I need insight on how to write these functions.
Note: This is only a snippet of my code.
There are a number of options. The main question is whether you want to write your own CSV parsing, or whether you want to use an existing library.
If this is an assignment, it might require you to write your own parser (doing that would probably be a bad idea in the real world, because real world CSV files can be very messy, but it might be fine if your input is very regular). If you were to use a library, the F# Data library is what most people in the F# community would use.
F# Data comes with a type provider called CsvProvider which infers the type of rows in a CSV file for you, so you do not have to write explicit type definitions. (Or you can still do that, but then load data into your structures using a simple transformation.)
F# Data also has CsvFile type, which just does the parsing, but then returns data as a sequence of rows (which are themselves arrays of string values). This might be nice if you just need something to take care of splitting the lines, but want to do the rest of the work.
If you wanted to write CSV parsing on your own, you can use File.ReadAllLines to read individual rows and then row.Split(',') to turn each row into an array of strings using , as the separator. This could work on your file - but it will break if there is any escaping in your file (for example Foo, "a, b", Bar is just three columns!
Related
How would I use a variable in a Go struct tag?
This works:
type Shape struct {
Type string `json:"type"`
}
This does not work:
const (
TYPE = "type"
)
type Shape struct {
Type string fmt.Sprintf("json:\"%s\"", TYPE)
}
In the first example, I am using a string literal, which works. In the second example, I am building a string using fmt.Sprintf, and I seem to be getting an error:
syntax error: unexpected name, expecting }
Here it is on the Go playground:
https://play.golang.org/p/lUmylztaFg
How would I use a variable in a Go struct tag? You wouldn't, it's not allowed by the language. You can't use a statement that evaluates at runtime in place of a compile time string literal for as an annotation to a field on a struct. As far as I know nothing of the sort works in any compiled language.
With the introduction of go generate, it is possible to do achieve this.
However, go generate essentially makes the compilation a 2 phase process. Phase 1 generates the new code, phase 2 compiles and links etc.
There are a few limitations with using go generate:
Your library will not be 'go get'-able unless you run go generate every time it is needed and check in the result, since go generate needs to be explicitly run before go build
This is a compile time process, so you will not be able to do it at run time using run time information. If you really must do this at run time, and in your case, you are just adding JSON serialization annotations, you could consider using a map.
String const/variable is not allowed in tag value to keep things simple and I support that. However with this limit, we need to use reflection to retrieve the tag value which is costly OR type string literals everywhere in the project, which may lead to bugs because of typos.
Solution
We can generate the tag values as string constant and then use this constant further in the project. It doesn't use reflection(saves performance cost), is more maintainable and removes the possibility of any bug because of typos.
ast package is an amazing tool to analyse and generate the go code. For example -
type user struct {
Name string `json:"name"`
Age int `json:"age"`
}
We can generated constants for user struct as below -
const (
UserNameJson = "name"
UserAgeJson = "age"
)
You may find tgcon helpful to generate the field tag value as const.
I would like something similar to what node-odata offers, but I do not want to wrap it around my database (I am using Cassandra and already have an Express app set up with routes, etc).
Currently, I grab data from the database (which will ultimately return a JSON object to the user) and then using the values passed in the query string I modify the results with JavaScript and pass the modified JSON object on through to the user.
I cannot pass in a query string like this http://localhost:3001/getSomeData?name=jim&age=21||eyeColor=red which includes logical operators in the query string, and would grab all data and filter it where the name is "jim", the age is "21" OR eyeColor is "red". So this would give me all Jims that have either eyeColor red and/or age of 21. If I used this age=21&&eyeColor=red I would expect to get all Jims that have BOTH eye color of red and are 21 years old.
I was thinking of using a custom query string that can be passed in (i.e. inclusive=age&inclusive=eyeColor appended at the end of the query string) and in Node, I would modify the filter results to treat these properties (age and eyeColor) as if they were passed in with the || OR operator). However, this is quite verbose, and I was hoping there was a library or another simpler implementation out there that solves this problem, or somehow lets me pass in simple logical operators into the query string.
I ended up using this library to achieve what I wanted: https://www.npmjs.com/package/jspath
It's well document and worked perfectly for my situation.
npm i querystringify //or
https://cdnjs.cloudflare.com/ajax/libs/qs/6.7.0/qs.min.js
//it will will return an object
const myObject = Qs.parse(location.search, {ignoreQueryPrefix: true});
//you can use object destructuring.
const {age,eyeColor}=Qs.parse(location.search, {ignoreQueryPrefix: true})
By default, parsing will include "?" too.
{ignoreQueryPrefix: true} this option will omit "?".
I'm new in creating jsons and having bais knowledge of java.
I'm trying to convert database table data to json.
Having option to store table data in any format of file than convert that into json.
Here is my table data.
Table: PKGS
Price, pd, Id, Level
1 , 266 , 59098 , 5
2 , 247 , 59098 , 5
I want my table data in this json format. Its just an example...to show level in JSON
"Id":59098
"pd":266
"Level":5
"price":1
"Id":59098
"pd":247
"Level":5
"price":2
In this json there is two loops are going If am not wrong. I was able to do it for one loop in ETL..but couldnt do it for two loops.
Not getting values for reimbursementId and packageId
Have goggled alot but couldn't find any code to understand properly and approach for the same.
Code tried little bit
FileInputStream inp = new FileInputStream("D:/json.xlsx" );
Workbook workbook = WorkbookFactory.create( inp );
Sheet sheet = workbook.getSheetAt( 0 );
JSONObject json = new JSONObject();
JSONArray rows = new JSONArray();
but dont know what to next !!
can anyone tell me how to do this ?
I advice you to use a specific tool. This is not a whole new case.
Try Talend Open Studio. It is not so complicate to use if you want to convert a file (CSV, JSON, Database directly, etc) to another. Please see TalendForge for basics.
In your case, you can connect to your database, and send all data in JSON.
Edit:
Your representation is not following the same logic than JSON. Here how I see it (and this is probably wrong because I can't understand)
If you just want Excel to JSON without any changes:
{
"rows":[
{
"Price":"1",
"pd":"266",
"Id":"59098",
"Level":"5"
},
{
"Price":"1",
"pd":"266",
"Id":"59098",
"Level":"5"
},
//and again and again
{
"Price":"2",
"pd":"247",
"Id":"59098",
"Level":"5"
}
]
}
If you want to reorganize, then define what you want. Try to imagine a sample of your data in a Java Object using ArrayList, int, String and subclass or even better in a JavaScript Object.
For the last example it will give you:
public class myJson{
ArrayList<myObject> rows;
with
public class myObject{
String Price;
String pd;
String Id;
String Level; //Or int, or date, or whatever
If you want to reorganize your data model, please give us this model.
Converting Excel file data to Json format is a a bit complex process, it depends on the structure of data, we do not have exact online tool as such so far...
custom code is required, there are various technologies available to be used, but best suited should be VBA, because VBA fits within Excel and can generate Json file quickly and flexible to edit code compared to any other technology that requires to automate to excel and import data and then process.
We can find there are various websites provide code to generate json from excel data, here is one such site looks expertise in this area. http://www.xlvba.net/tools/excel-automation-to-convert-excel-data-to-json-format.html
Ragavendra
According to http://www.cocos2d-x.org/wiki/Value,
Value can handle strings as well as int, float, bool, etc.
I'm confused when I have to make a choice between using
std::string
or
Value
In what circumstances should I use Value over std::string, and vice versa??
I think you have misunderstood the Value object. As written in the documentation you linked to:
cocos2d::Value is a wrapper class for many primitives ([...] and std::string) plus [...]
So really Value is an object that wraps a bunch of other types of variables, which allows cocos2d-x to have loosely-typed structures like the ValueMap (a hash of strings to Values - where each Value can be a different type of object) and ValueVector (a list of Values).
For example, if you wanted to have a configuration hash with keys that are all strings, but with a bunch of different values - in vanilla C++, you would have to create a separate data structure for each type of value you want to save, but with Value you can just do:
unordered_map<std::string, cocos2d::Value> configuration;
configuration["numEnemies"] = Value(10);
configuration["gameTitle"] = Value("Super Mega Raiders");
It's just a mechanism to create some loose typing in C++ which is a strongly-typed language.
You can save a string in a Value with something like this:
std::string name = "Vidur";
Value nameVal = Value(name);
And then later retrieve it with:
std::string retrievedName = nameVal.asString();
If you attempt to parse a Value as the wrong type, it will throw an error in runtime, since this is isn't something that the compiler can figure out.
Do let me know if you have any questions.
I'm using webwrite to post to an api. One of the field names in the json object I'm trying to setup for posting is odata.metadata. I'm making a struct that looks like this for the json object:
json = struct('odata.metadata', metadata, 'odata.type', type, 'Name', name,);
But I get an error
Error using struct
Invalid field name "odata.metadata"
Here's the json object I'm trying to use in Matlab. All strings for simplicity:
{
"odata.metadata": "https://website.com#Element",
"odata.type": "Blah.Blah.This.That",
"Name": "My Object"
}
Is there a way to submit this json object or is it a lost cause?
Field names are not allowed to have dots in them. The reason why is because this will be confused with accessing another nested structure within the structure itself.
For example, doing json.odata.metadata would be interpreted as json being a struct with a member whose field name is odata where odata has another member whose field name is metadata. This would not be interpreted as a member with the combined field name as odata.metadata. You're going to have to rename the field to something else or change the convention of your field name slightly.
Usually, the convention is to replace dots with underscores. An automated way to take care of this if you're not willing to manually rename the field names yourself is to use a function called matlab.lang.makeValidName that takes in a string and converts it into a valid field name. This function was introduced in R2014a. For older versions, it's called genvarname.
For example:
>> matlab.lang.makeValidName('odata.metadata')
ans =
odata_metadata
As such, either replace all dots with _ to ensure no ambiguities or use matlab.lang.makeValidName or genvarname to take care of this for you.
I would suggest using a a containers.Map instead of a struct to store your data, and then creating your JSON string by iterating over the Map filednames and appending them along with the data to your JSON.
Here's a quick demonstration of what I mean:
%// Prepare the Map and the Data:
metadata = 'https://website.com#Element';
type = 'Blah.Blah.This.That';
name = 'My Object';
example_map = containers.Map({'odata.metadata','odata.type','Name'},...
{metadata,type,name});
%// Convert to JSON:
JSONstr = '{'; %// Initialization
map_keys = keys(example_map);
map_vals = values(example_map);
for ind1 = 1:example_map.Count
JSONstr = [JSONstr '"' map_keys{ind1} '":"' map_vals{ind1} '",'];
end
JSONstr =[JSONstr(1:end-1) '}']; %// Finalization (get rid of the last ',' and close)
Which results in a valid JSON string.
Obviously if your values aren't strings you'll need to convert them using num2str etc.
Another alternative you might want to consider is the JSONlab FEX submission. I saw that its savejson.m is able to accept cell arrays - which can hold any string you like.
Other alternatives may include any of the numerous Java or python JSON libraries which you can call from MATLAB.
I probably shouldn't add this as an answer - but you can have '.' in a struct fieldname...
Before I go further - I do not advocate this and it will almost certainly cause bugs and a lot of trouble down the road... #rayryeng method is a better approach
If your struct is created by a mex function which creates a field that contains a "." -> then you will get what your after.
To create your own test see the Mathworks example and modify accordingly.
(I wont put the full code here to discourage the practice).
If you update the char example and compile to test_mex you get:
>> obj = test_mex
obj =
Doublestuff: [1x100 double]
odata.metadata: 'This is my char'
Note: You can only access your custom field in Matlab using dynamic fieldnames:
obj.('odata.metadata')
You need to use a mex capability to update it...