Selecting strings by numeric character values

Questions
1

“{190012}”, “{90013}”, “{80016}”, “{90022}”, “{90034}”, “{90042}”, \
“{90102}”, “{90106}”, “{90115}”, “{50131}”, “{90132}”, “{90137}”, \
“{90153}”, “{90214}”, “{90222}”, “{90226}”, “{90230}”, “{90234}”, \
“{90239}”, “{90247}”, “{90304}”, “{90306}”, “{70312}”, “{90316}”, \

"{90323}", "{90325}", "{90328}", "{90331}", "{90332}", "{90333}",

How to select numbers that begin with specified digit for example 8 ?These numbers are not possessed of having attribute of numbers yet.They are strings .

2

Hey Marek,

The following code will do what you want. Now I have a list of number and I want to take out the string that contains a number begins with 4.

Cases[{"{1234}", "{4321}"}, 
 x_ /; (IntegerDigits@ToExpression[x][[1]])[[1]] == 4
 ]

The main body is Case[ <my list>, pattern]. For our default pattern “x_”, it matches everything so I need to add a condition here (“/;”), which is “the first digit be 4” .
In the condition, I convert the element into a computable expression (ToExpression[“{123}”] → {123} = List[123]). Then I take the first element from the list, from last example, yields an integer, 123. IntegerDigits breaks this number into {1,2,3}.
Finally, I check if the first element ( {1,2,3} [[1]] → 1) matches 4.

3

An alternative approach:

Select[{"{1234}", "{4321}"}, Characters[#][[2]] == "4" &]

A further possibility would be to thrown in a ToExpression on Characters, if the comparison needs to be numeric.

4

An other approach is to use Pick and StringMatchQ. Say we have this.

j = {"190012", "90013", "80016", "90022", "50131", "865543",
"78880999", "8003003"}

Then we can use this

Pick[j, StringMatchQ[j, "8" ~~ ___ ~~ ___]]

with this output

{"80016", "865543", "8003003"}

Paul.

5

StringCases use of StringPattern can also pull out matches with sub-strings

StringCases[yourlst, "{8" ~~ __]

{{}, {}, {“{80016}”}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}}

StringCases[yourlst, "{" ~~ num : ("8" ~~ __) ~~ "}" :> num]

{{}, {}, {“80016”}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}}

Flatten to get rid of empty sub-string results

Flatten@StringCases[yourlst, "{" ~~ num : ("8" ~~ __) ~~ "}" :> num]

{“80016”}

6

Here are 3 another options, with time test:

list={"{190012}","{90013}","{80016}","{90022}","{90034}","{90042}","{90102}","{90106}","{90115}","{50131}","{90132}","{90137}","{90153}","{90214}","{90222}","{90226}","{90230}","{90234}","{90239}","{90247}","{90304}","{90306}","{70312}","{90316}" };
listBig=Join@@ConstantArray[list,{100000}];

Select[listBig,StringMatchQ[#,"{8*}"]&];//AbsoluteTiming//First
Cases[listBig,x_/;StringMatchQ[x,"{8*}"]];//AbsoluteTiming//First
Extract[listBig,Position[listBig,x_/;StringMatchQ[ToString@x,"{8*}"],{1}]];//AbsoluteTiming//First

1.493229
1.456528
4.747536