[R] Sandard deviation calculation

[(Ted Harding)]

On 26-Oct-09 09:44:55, ms.com wrote:
> 
> Dear all
> I am trying to learn R
> I was trying to calculate standard deviation
> here are the commands and outputs in R
>> sd(Ht_cm[type=='SD'])[1] 3.283605
>> sd(Ht_cm[from_treeline=='above'])[1] 16.83289
>> sd(Ht_cm[type=='SD'][from_treeline=='above'])[1] NA
> 
> the problem is that, i could not understand why the third command could
> not give any result.
> please help me out
> thanking you
> Regard
> MS
> Nepal

This suggests that either you have only one observation in the
third case, or there is an NA amongst them.

What are the values of

  length((Ht_cm[type=='SD'][from_treeline=='above'])[1])

  sum(is.na((Ht_cm[type=='SD'][from_treeline=='above'])[1]))

  sum((type=='SD')&(from_treeline=='above'))

  sum(type=='SD')

  sum(from_treeline=='above')

The answers to these may provide adequate clues to diagnose
the reason.

Ted.

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Date: 26-Oct-09                                       Time: 14:28:38
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