# Re: [R] using "mean" in by(x,y,mean)

From: Sundar Dorai-Raj <sundar.dorai-raj_at_pdf.com>
Date: Thu 15 Jul 2004 - 06:52:28 EST

> Dear list friends
>
> I fail to understand how to find means for multiple groups using the
> by() function. Help would be appreciated. Thanks.
> Bill
>
>
> x <- runif(20,0,10)
> group <- rep(c("A","B"),10)
> df <-data.frame(x,group)
> #df #show the data
>
> rm(x,group)
> attach(df)
>
> sd(x) # sd is defined
> mean(x) #so is mean
>
> by(x,group,sd) #this works for both groups
> by(x,group,mean) #this does not
>
>
> produces this output:
>
>

```>>  x <- runif(20,0,10)
>>  group <- rep(c("A","B"),10)
>>  df <-data.frame(x,group)
>>  #df            #show the data
>>
>>  rm(x,group)
>>  attach(df)
>>
>>  sd(x)       # sd is defined
```

>
>  2.952699
>
```>>  mean(x)     #so is mean
```

>
>  5.026441
>
```>>
>>  by(x,group,sd)   #this works for both groups
```

>
> INDICES: A
>  2.813504
> ------------------------------------------------------------------------------------------------------------
>
> INDICES: B
>  3.236663
>
```>>  by(x,group,mean)  #this does not
```

>
> Error in FUN(X[[as.integer(1)]], ...) : couldn't find function "FUN"
>
>
> I am using a Mac OS 10.3.4 running R 1.9.1

Hi Bill,

Works for me. Do you have a local "mean" defined? Try rm(mean) and re-try.

> R.version

_
platform i386-pc-mingw32

```arch     i386
os       mingw32
```

system i386, mingw32
status
major 1
minor 9.1
year 2004
month 06
day 21
language R

--sundar

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