Simplify IF-clause and find name of Variable in LINQ select statement

Question

I am trying to find out which List<int> out of many has a certain amount of elements

Example input:

List<int> list_1 = Enumerable.Range(1, 299).ToList();
List<int> list_2 = Enumerable.Range(1, 300).ToList();
List<int> list_3 = Enumerable.Range(1, 300).ToList();
List<int> list_4 = Enumerable.Range(1, 297).ToList();

What I need is to log the name of the list and the amount of items if it has less than let's say 300 values. Now I could do of course a single if clause for every list:

if (list_1.Count != 300)
{
    //log name and number of items
}
if(list_2 ... and so on)

Question: Is there a more elegant way of finding out this information?

I tried a LINQ solution and put all Lists into one for filtering. But in this my problem is that I cannot get the name:

List<List<int>> allLists = new List<List<int>>();

allLists.Add(list_1);
allLists.Add(list_2);
allLists.Add(list_3);
allLists.Add(list_4);

string logRes = String.Join(" ", allLists.Where(x=>x.Count < 300)
        .Select(x=> String.Format("Name: {0} Amount: {1}", nameof(x), x.Count)));

It returns:

Name: x Amount: 299 Name: x Amount: 297

Question 2: How can I get the name of the evil list in the collection?

Would not make more sense using a `Dictionary>` instead of a list of lists? The key may contain the name of the list. — Federico Dipuma, May 08 '17 at 14:59
If you are using C# 6.0 you can also make use of NameOf expressions: http://gigi.nullneuron.net/gigilabs/c-6-preview-nameof-expressions/ However i agree that a dictionary would be a much more elegant solution here. — Master Yoda, May 08 '17 at 15:01
@MasterYoda: he uses namof, but that doesnt help in the LINQ query — Tim Schmelter, May 08 '17 at 15:04
@TimSchmelter Ah i see that now. Sorry I must have overlooked that. — Master Yoda, May 08 '17 at 15:05

score 3 · Accepted Answer · edited May 23 '17 at 12:02

3

Either use reflection or a different collection like f.e. aDictionary<string, List<int>>:

var listNames = new Dictionary<string, List<int>>();
listNames.Add(nameof(list_1), list_1);
listNames.Add(nameof(list_2), list_2);
listNames.Add(nameof(list_3), list_3);
listNames.Add(nameof(list_4), list_4);

string logRes = String.Join(" ", listNames
    .Where(kv => kv.Value.Count < 300)
    .Select(kv => $"Name: {kv.Key} Amount: {kv.Value.Count}"));

edited May 23 '17 at 12:02

Community

1
1

answered May 08 '17 at 15:02

Tim Schmelter

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Thank you for the dictionary suggestion. Is this the best way to avoid multiple if-clauses? – Mong Zhu May 09 '17 at 06:26
@MongZhu: specify _best_, in my opinion its a readable and concise version, yes. – Tim Schmelter May 09 '17 at 07:47
trying to specify: less code but still readable. It gets pretty wild to read if I would have 10 lists for example. But then again may be I should rethink the design of saving the data in the first place maybe. I like your solution, thanx again – Mong Zhu May 09 '17 at 07:51

sachin · Answer 2 · 2017-05-08T15:24:54.097

0

You may modify your code to include the names of lists along with actual lists:

Dictionary<string, List<int>> allLists = new Dictionary<string, List<int>>();

allLists.Add("list_1", list_1);
allLists.Add("list_2", list_2);
allLists.Add("list_3", list_3);
allLists.Add("list_4", list_4);

string logRes = String.Join(" ", allLists
    .Where(x => x.Value.Count < 300)
    .Select(x => String.Format("Name: {0} Amount: {1}", x.Key, x.Value.Count)));

edited May 08 '17 at 15:24

answered May 08 '17 at 15:05

sachin

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Your answer is exact the same as @Tim Schmelter.. But he was 4 mintues before you.. – Sean Stayns May 08 '17 at 15:08
@SeanStayn Well not exactly same, that one is going to work only after C# 6.0. Looks like I took quite some time in typing my answer. – sachin May 08 '17 at 15:23

Simplify IF-clause and find name of Variable in LINQ select statement

2 Answers2