[R] Sandard deviation calculation

[Duncan Murdoch]

On 27/10/2009 2:58 PM, marcos carvajalino wrote:
> Dear ms.
> 
> The most possible reason for this:
> 
>> 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 	
> 
> is that you're trying to calculate sd over a vector where a NA (Not
> available) value is contained, that is, you have an empty cell, a
> different type of data or no data satisfies your condition, try:
> 
>> sd(Ht_cm[type=='SD'][from_treeline=='above'],na.rm=T)
> 
> That should do it...

That's legal syntax, but it is very unlikely to be correct.  Hadley gave 
good advice (modulo his typo).

Duncan Murdoch