R help - Jun 2011 - How do I make proper use of the by() function?

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Name: inte tillg?nglig
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You may want to read about several "apply" functions. They may help
you do
what you are trying.

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
Behalf Of Fredrik Karlsson
Sent: Saturday, June 11, 2011 3:13 AM
To: R-Help List
Subject: [R] How do I make proper use of the by() function?

Dear list,

I have a function that uses values from two vectors  and spits out one new
vector  based on all the values of the two original vectors, and with the
same length as them.
Ok, I would now like to be able to apply that function simply on two columns
in a data frame, divided by the levels of factors in the data frame.

I'm trying to use by() for this, but the output is too hard to use. What I
am doing is this:

by(df, list(df$Factor1,df$Factor2),function(x)
my_function(x$col1,x$col2),simplify=TRUE)

and the output is too complex to be used in a simple way. Actually, I just
want something like a data frame, where the results vectors are placed in
one column and the conditions under which they were produced (i.e. the
values of the factors according to which the data set were divided) in other
columns.

This does not seem to be provided by by(), and aggregate only provides me
with the ability to use values from one column, right?
So, are there other functions I could use?

Thanks!

/Fredrik

--
"Life is like a trumpet - if you don't put anything into it, you
don't get
anything out of it."

	[[alternative HTML version deleted]]

______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Hi
> [R] How do I make proper use of the by() function?
> 
> Dear list,
> 
> I have a function that uses values from two vectors  and spits out one 
new
> vector  based on all the values of the two original vectors, and with 
the
> same length as them.
> Ok, I would now like to be able to apply that function simply on two 
columns
> in a data frame, divided by the levels of factors in the data frame.
> 
> I'm trying to use by() for this, but the output is too hard to use.
What
I
> am doing is this:
> 
> by(df, list(df$Factor1,df$Factor2),function(x)
> my_function(x$col1,x$col2),simplify=TRUE)
by(df, list(df$Factor1,df$Factor2),function(x) 
my_function(x$col1,x$col2),simplify=TRUE)
Error in df$Factor1 : object of type 'closure' is not subsettable

I get this kind of error which is because I do not have any df object 
other than df function from stats package.

If I understand correctly you want maybe either aggregate or ave
> milan
   pc lot bettong    bet  sira vyber betctc
1   1  56   89.95 109.25 3.000     b  88.37
2   2  66   86.87 100.96 3.156     a     NA
3   3  84   93.91 101.21 3.120     a     NA
4   4  89   89.48 100.00 3.010     a     NA
5   5  41  110.15 116.92 3.597     b 106.37
6   6  44   96.53 106.54 3.057     b     NA
7   7  47   94.94 104.91 2.857     b     NA
8   8  62   90.30 111.05 3.210     b     NA
9   9  64   96.41 102.56 3.180     a  90.79
10 10  65   95.04 101.15 3.200     a     NA
11 11  57   88.27 104.71 3.060     b     NA
12 13  74   91.98 104.93 3.470     a     NA
> aggregate(milan[,2:5], list(milan$vyber), sum) 
  Group.1 lot bettong    bet   sira
1       a 442  553.69 610.81 19.136
2       b 307  570.14 653.38 18.781
> sapply(milan[,2:5], function(x) ave(x, milan$vyber, "sum"))
           lot  bettong      bet     sira
 [1,] 51.16667 95.02333 108.8967 3.130167
 [2,] 73.66667 92.28167 101.8017 3.189333
 [3,] 73.66667 92.28167 101.8017 3.189333
 [4,] 73.66667 92.28167 101.8017 3.189333
 [5,] 51.16667 95.02333 108.8967 3.130167
 [6,] 51.16667 95.02333 108.8967 3.130167
 [7,] 51.16667 95.02333 108.8967 3.130167
 [8,] 51.16667 95.02333 108.8967 3.130167
 [9,] 73.66667 92.28167 101.8017 3.189333
[10,] 73.66667 92.28167 101.8017 3.189333
[11,] 51.16667 95.02333 108.8967 3.130167
[12,] 73.66667 92.28167 101.8017 3.189333

But maybe I am wrong, I still only try to learn mind reading.
> 
> and the output is too complex to be used in a simple way. Actually, I 
just
> want something like a data frame, where the results vectors are placed 
in
> one column and the conditions under which they were produced (i.e. the
> values of the factors according to which the data set were divided) in 
other
> columns.
> 
> This does not seem to be provided by by(), and aggregate only provides 
me
> with the ability to use values from one column, right?
> So, are there other functions I could use?
> 
> Thanks!
> 
> /Fredrik
> 
> -- 
> "Life is like a trumpet - if you don't put anything into it, you
don't
get
> anything out of it."
> 
>    [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.