[R] Sandard deviation calculation

[marcos carvajalino]

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...

-- 
Marcos Antonio Carvajalino Fernández
Estudiante de Ingeniería Ambiental y Sanitaria
Universidad del Magdalena, Colombia