Re: Select x s.t. y>10

• To: mathgroup at smc.vnet.net
• Subject: [mg13982] Re: [mg13957] Select x s.t. y>10
• From: BobHanlon at aol.com
• Date: Sat, 12 Sep 1998 16:59:07 -0400
• Sender: owner-wri-mathgroup at wolfram.com

```data = Table[{Random[], 10 Random[]}, {1000}];

To select the first x for which the corresponding y is greater than
five:

Select[data, #[[2]]>5&][[1, 1]]//Timing

{0.0666667 Second,0.190228}

Cases[data, {x_, y_/;y>5}][[1, 1]]//Timing

{0.0666667 Second,0.190228}

Cases[data, {x_, y_/;y>5}->x][[1]]//Timing

{0.0666667 Second,0.190228}

Cases[data, {x_, y_}?(#[[2]]>5&)][[1, 1]]//Timing

{0.0833333 Second,0.190228}

Cases[data, {x_, y_}?(#[[2]]>5&)->x][[1]]//Timing

{0.116667 Second,0.190228}

firstCase[theList_List, gtr_?NumericQ] :=
Module[{selected},
selected = Cases[theList, {x_, y_/;y>gtr}];
If[Length[selected] > 0, selected[[1, 1]], {}]]

firstCase[data, 5]

0.190228

Bob Hanlon

In a message dated 9/11/98 6:47:45 PM, jgill at vbimail.champlain.edu
wrote:

>I came across what seems like it should be a simple little function, but
>could not come up with a clever way to implement it.  Generally, what I
>am trying to do is take a list of lists of length 2 ie a list of x,y
>coordinates, and Select x values based on some criterion for y.  For
>example I want to select the first x value for which the corresponding
>y is greater than 5.
>I can write a function using Position and Take etc. , but there must be
>a clever,and more efficient way to do this.  Any thoughts... Jason

```

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