Looking for specific data in .txt file

Question

I've the following code:

Import["test.txt"]

And it gives me:

1,10

2,20

3,30

4,40

5,50

6,60

7,70

8,80

9,90

10,100

11,110

12,120

13,130

14,140

15,150

16,160

17,170

18,180

19,190

But I only want the time values $8,9,10$ how can I improve my code so that only those times are printed in my notebook?

---

I used this code but that does not work, but why?

s = Import["test.txt"];
data = ToExpression@StringSplit[
    Rest[
     StringSplit[s, {""}]
     ],
    ","];
Select[data, MemberQ[{8, 9, 10}, #[[1]]] &]

Answer 1

The following seems to work:

data = Table[{i, i*10}, {i, 1, 19}];

which mimics what final form of the data should look like

Select[data, MemberQ[{8, 9, 10}, #[[1]]] &]
(*{{8, 80}, {9, 90}, {10, 100}}*)

I am not certain if the contents of your test file are as you posted or there are just typos. But using ImportString[] to sit in for Import[] for immediate results

    data2 = ImportString["1,10
2,20
3,30
4,40
5,50
6,60
7,70
8,80
9,90
10,100
11,110 
12,120
13,130
14,140
15,150
16,160
17,170
18,180
19,190", "CSV"];
Select[data2, MemberQ[{8, 9, 10}, #[[1]]] &]
(*{{8, 80}, {9, 90}, {10, 100}}*)

So Try

data = Import["test.txt", "CSV"]

Answer 2

If you take the code you have given and evaluate it one part at a time, starting from the inside, and you'll find it doesn't do what you want it to (it starts by splits on every character and then drops the first character for some reason).

How about this function:

selectNumberLines[textData_, num_] :=  Pick[StringSplit[textData, "\n"], 
StringContainsQ[StringSplit[textData, "\n"], StartOfLine ~~ ToString[num] ~~ "," ~~ ___]]

It splits the block of text from the Input into individual lines before finding those that start with the number that you give.

selectNumberLines[s, #] & /@ {8, 9, 10}
 (* {{"8,80"}, {"9,90"}, {"10,100"}}  *)

If your data is always of the form "number, stuff you want", you could try this to get only the later parts:

selectNumberLinesValues[textData_, num_] := 
 ToExpression@Last@Last@StringSplit[selectNumberLines[textData,num], ","]

selectNumberLinesValues[s, #] & /@ {8, 9, 10}
(* {80, 90, 100} *)

But you need to be careful with matching patterns like this.