[R] Null values In R.

[paul murima]

Hi everyone.

I am having problems with NULL values. I understand in R one can
command the program to skip null values.
Can some one help me on the command line for that.
Do i enter is as part of the string in:
a<- read.table("filename.csv", header = T, row.names=1, sep=",");

My problem is largely when i attempt to use correlation for my data...
xcc <- cor(a);

The error i get is as follows

Error in cor(a) : missing observations in cov/cor
In addition: Warning message:
In cor(a) : NAs introduced by coercion

Regards

Paul Murima

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[paul murima]

[Daniel Malter]

Hi, for your cor() command you will want to specify the "use" argument as
either "complete.obs" or as "pairwise.complete.obs". The difference between
the two is that the former only uses those observations for which ALL
information in "a" is available, whereas the latter uses information that is
available for all pairwise comparisons between variables in "a". For the
example below, use="c" would exclude observations 6 and 5, whereas use="p"
would exclude observations 6 and 5 for correlations between x and y, and x
and z, but it would only exclude observation 5 for the correlation between y
and z

x=c(1,2,3,4,5,NA)
y=c(2,3,3.5,4.75,NA,7)
z=c(5,8,7,6,NA,11)

a=data.frame(x,y,z)

cor(a)
cor(a,use="c")
cor(a,use="p")

Cheers,
Daniel

-------------------------
cuncta stricte discussurus
-------------------------

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Von: r-help-...@r-project.org [mailto:r-help-...@r-project.org] Im
Auftrag von paul murima
Gesendet: Tuesday, December 02, 2008 11:33 PM
An: r-h...@r-project.org
Cc: r-h...@stat.math.ethz.ch
Betreff: [R] Null values In R.

[Dieter Menne]

paul murima wrote:
>
>
> My problem is largely when i attempt to use correlation for my data...
> xcc <- cor(a);
>
> The error i get is as follows
>
> Error in cor(a) : missing observations in cov/cor
>

As Daniel suggested, it is always best to use the function's parameter to
handle NULLs. In other cases, it could help to do

a <- na.omit(a)

but be careful: this may throw away to many rows when you have more than 2
columns.

Dieter

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