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margherita ferrucci

TakeWhile and Select

margherita ferrucci, Université Paris Est
Posted 9 years ago
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I have this list: 

geo = {{0.107885, 0.21577, 0.313393, 0.411015, 0.499351, 0.587688, 0.667621,
   0.747554, 0.819884, 0.892213, 0.981434, 1.07066, 1.15988, 1.2491, 
  1.33832, 1.42754, 1.51676, 1.60598, 1.6952}}

If I SELECT the elements Lato1 and Lato2, with the the command below, the command sequence runs. 

B=0.5
geo = Flatten [geo]
Lato1 = Select [geo, #<=B &] 
Latoo2 = Select[geo , B<#<1.6. &]

On the contrary if I use the command TakeWhile, it doesen't run for Lato2. Why??

B=0.5
geo = Flatten [geo]
Lato1 = TakeWhile [geo, #<=B &] 
Lato2 = TakeWhile [geo , B<#<1.6. &]

Thanks
POSTED BY: margherita ferrucci
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Thank you!
POSTED BY: margherita ferrucci
Girish Arabale
Girish Arabale
Posted 9 years ago

By definition,

Select[list,crit]

picks out ALL elements of the list for which crit is True.

whereas 

TakeWhile[list,crit]

gives elements of the list from the beginning for which crit is True but stops at the value for which crit is not true. It doesn't evaluate further.

For e.g.

Select[{a, 1, 2, 3, b, c, 4, d, 5}, IntegerQ]
{1, 2, 3, 4, 5}

But

TakeWhile[{a, 1, 2, 3, b, c, 4, d, 5}, IntegerQ]
{}
POSTED BY: Girish Arabale
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