Convert ordered comma separated list into tuples with ordered element number (a la SQL SPLIT

I can't seem to find a ready answer to this, or even if the question has ever been asked before, but I want functionality similar to the SQL STRING_SPLIT functions floating around, where each item in a comma separated list is identified by its ordinal in the string.

Given the string "abc,xyz,def,tuv", I want to get a list of tuples like:

<1, "abc">
<2, "xyz">
<3, "def">
<4, "tuv">

Order is important, and I need to preserve the order, and be able to take the list and further join it with another list using linq, and be able to preserve the order. For example, if a second list is <"tuv", "abc">, I want the final output of the join to be:

<1, "abc">
<4, "tuv">

Basically, I want the comma separated string to determine the ORDER of the end result, where the comma separated string contains ALL possible strings, and it is joined with an unordered list of a subset of strings, and the output is a list of ordered tuples that consists only of the elements in the second list, but in the order determined by the comma separated string at the beginning.

I could likely figure out all of this on my own if I could just get a C# equivalent to all the various SQL STRING_SPLIT functions out there, which do the split but also include the ordinal element number in the output. But I've searched, and I find nothing for C# but splitting a string into individual elements, or splitting them into tuples where both elements of the tuple are in the string itself, not generated integers to preserve order.

The order is the important thing to me here. So if an element number isn't readily possible, a way to inner join two lists and guarantee preserving the order of the first list while returning only those elements in the second list would be welcome. The tricky part for me is this last part: the result of a join needs a specific (not easy to sort by) order. The ordinal number would give me something to sort by, but if I can inner join with some guarantee the output is in the same order as the first input, that'd work too.

CodePudding user response：

If you wanted to stick to something SQL like here is how to do it with linq operators. The Select method has a built in index param you can make use of. And you can use IntersectBy to perform an easy inner join.

using System.Linq;
string str = "abc,xyz,def,tuv";
string str2 = "abc,tuv";
var secondList = str2.Split(',');

var tups = str.Split(',')
    .Select((x, i) => { return (i   1, x); })
    .IntersectBy(secondList, s=>s.Item2) //Filter down to only the strings found in both.
    .ToList();

foreach(var tup in tups)
{
    Console.WriteLine(tup);
}

CodePudding user response：

This will get you list of tuples

var input = "abc,xyz,def,tuv";
string[] items = input.Split(',');
var tuples = new List<(int, string)>();
for (int i = 0; i < items.Length)
{
    tuples.Add(((i   1), items[i]));
}

if then you want to add list of "tuv" and "abc" and keep 1, you probably want to "Left Join". But I am not sure, how you can do using LINQ because you first need to iterate the original list of tuples and assign same int. Then join. Or, you can join first and then assign int but technically, order is not guaranteed. However, if you assign int first, you can sort by it in the end.

I am slightly confused by "and be able to take the list and further join it with another list using linq". Join usually means aggregate result. But in your case it seem you demanding segment, not joined data.

CodePudding user response：

Not 100% sure what you're after, but here's an attempt:

string[] vals = new[] { "abc", "xyz", "dev", "tuv"};

string[] results = new string[vals.Length];

int index = 0;

for (int i = 0; i < vals.Length; i  )
{
    results[i] = $"<{  index},\"{vals[i]}\">";
}

foreach (var item in results)
{
    Console.WriteLine(item);
}

This produces:

<1,"abc">
<2,"xyz">
<3,"dev">
<4,"tuv">

CodePudding user response：

with LINQ

string inputString = "abc,xyz,def,tuv";
var output = inputString.Split(',')
.Select((item, index) => { return (index   1, item); });

now you can use the output list as you want to use.

CodePudding user response：

Given the example

For example, if a second list is <"tuv", "abc">, I want the final output of the join to be:

<1, "abc"> <4, "tuv">

I think this might be close?

List<string> temp = new List<string>() { "abc", "def", "xyz", "tuv" };
List<string> temp2 = new List<string>() { "dbc", "ace", "zyw", "tke", "abc", "xyz" };
var intersect = temp.Intersect(temp2).Select((list, idx) => (idx 1, list));

This produces an intersect result that has the elements from list 1 that are also in list 2, which in this case would be:

<1, "abc">
<2, "xyz">

If you want all the elements from both lists, switch the Intersect to Union.