R help - Jul 2010 - using string variable as order() function argument

Hello,

In my script I would like to use a loop, which sorts the dataframe 
according to different columns, pointed by the string variable.

     id col1  col2  col3
1   10    0    4      8
2   11    1    2      2
3   12    0    8      3
4   13    0    5      5

Usually the order() function can be used like this:

sorted = mytable**[order(column3) , ]

which results in properly sorted table:
**

     id col1  col2  col3
2   11    1    2      2
3   12    0    8      3
4   13    0    5      5
1   10    0    4      8

**But when trying to use a string variable instead of "column3" name:

columnname = "column3"
**sorted = mytable**[order(columnname) , ]**

this command is not properly evaluated and the effect is somewhat strange.

Would you suggest some solution?

Thanks a lot!

Mirek

Hello,

In my script I would like to use a loop, which sorts the dataframe 
according to different columns, pointed by the string variable.

     id col1  col2  col3
1   10    0    4      8
2   11    1    2      2
3   12    0    8      3
4   13    0    5      5

Usually the order() function can be used like this:

sorted = mytable[order(column3) , ]

which results in properly sorted table:

     id col1  col2  col3
2   11    1    2      2
3   12    0    8      3
4   13    0    5      5
1   10    0    4      8

But when trying to use a string variable instead of "column3" name:

columnname = "column3"
sorted = mytable[order(columnname) , ]

this command is not properly evaluated and the effect is somewhat strange.

Would you suggest some solution?

Thanks a lot!

Mirek

On 26/07/2010 2:56 PM, mirek wrote:
> Hello,
>
> In my script I would like to use a loop, which sorts the dataframe 
> according to different columns, pointed by the string variable.
>
>      id col1  col2  col3
> 1   10    0    4      8
> 2   11    1    2      2
> 3   12    0    8      3
> 4   13    0    5      5
>
> Usually the order() function can be used like this:
>
> sorted = mytable[order(column3) , ]
>
> which results in properly sorted table:
>
>      id col1  col2  col3
> 2   11    1    2      2
> 3   12    0    8      3
> 4   13    0    5      5
> 1   10    0    4      8
>
> But when trying to use a string variable instead of "column3"
name:
>
> columnname = "column3"
> sorted = mytable[order(columnname) , ]
>
> this command is not properly evaluated and the effect is somewhat strange.
The argument to order() should be a vector whose sort order is to be 
returned.  So you just need to extract one column from the dataframe, e.g.

column <- mytable[, columnname]
sorted <- mytable[order(column) , ]

Duncan Murdoch

Hi,

Is this what you want?

##############
mytable <- read.table(textConnection("
id col1  col2  col3
10    0    4      8
11    1    2      2
12    0    8      3
13    0    5      5
"), header = TRUE)

mytable

columnname <- "col3"

mytable[order(mytable[, columnname]), ]
###################

Josh

On Mon, Jul 26, 2010 at 11:54 AM, mirek wyczesany
<miroslaw.wyczesany at uj.edu.pl> wrote:
> Hello,
>
> In my script I would like to use a loop, which sorts the dataframe
according
> to different columns, pointed by the string variable.
>
> ? ?id col1 ?col2 ?col3
> 1 ? 10 ? ?0 ? ?4 ? ? ?8
> 2 ? 11 ? ?1 ? ?2 ? ? ?2
> 3 ? 12 ? ?0 ? ?8 ? ? ?3
> 4 ? 13 ? ?0 ? ?5 ? ? ?5
>
> Usually the order() function can be used like this:
>
> sorted = mytable**[order(column3) , ]
>
> which results in properly sorted table:
> **
>
> ? ?id col1 ?col2 ?col3
> 2 ? 11 ? ?1 ? ?2 ? ? ?2
> 3 ? 12 ? ?0 ? ?8 ? ? ?3
> 4 ? 13 ? ?0 ? ?5 ? ? ?5
> 1 ? 10 ? ?0 ? ?4 ? ? ?8
>
> **But when trying to use a string variable instead of "column3"
name:
>
> columnname = "column3"
> **sorted = mytable**[order(columnname) , ]**
>
> this command is not properly evaluated and the effect is somewhat strange.
>
> Would you suggest some solution?
>
> Thanks a lot!
>
> Mirek
>
> ______________________________________________
> 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.
>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

Try this:
> mytable
  id col1 col2 col3
1 10    0    4    8
2 11    1    2    2
3 12    0    8    3
4 13    0    5    5
> colName <- 'col3'
> mytable[order(mytable[[colName]]),]
  id col1 col2 col3
2 11    1    2    2
3 12    0    8    3
4 13    0    5    5
1 10    0    4    8
> colName <- 'id'
> mytable[order(mytable[[colName]]),]
  id col1 col2 col3
1 10    0    4    8
2 11    1    2    2
3 12    0    8    3
4 13    0    5    5
>


On Mon, Jul 26, 2010 at 2:54 PM, mirek wyczesany
<miroslaw.wyczesany at uj.edu.pl> wrote:
> Hello,
>
> In my script I would like to use a loop, which sorts the dataframe
according
> to different columns, pointed by the string variable.
>
> ? ?id col1 ?col2 ?col3
> 1 ? 10 ? ?0 ? ?4 ? ? ?8
> 2 ? 11 ? ?1 ? ?2 ? ? ?2
> 3 ? 12 ? ?0 ? ?8 ? ? ?3
> 4 ? 13 ? ?0 ? ?5 ? ? ?5
>
> Usually the order() function can be used like this:
>
> sorted = mytable**[order(column3) , ]
>
> which results in properly sorted table:
> **
>
> ? ?id col1 ?col2 ?col3
> 2 ? 11 ? ?1 ? ?2 ? ? ?2
> 3 ? 12 ? ?0 ? ?8 ? ? ?3
> 4 ? 13 ? ?0 ? ?5 ? ? ?5
> 1 ? 10 ? ?0 ? ?4 ? ? ?8
>
> **But when trying to use a string variable instead of "column3"
name:
>
> columnname = "column3"
> **sorted = mytable**[order(columnname) , ]**
>
> this command is not properly evaluated and the effect is somewhat strange.
>
> Would you suggest some solution?
>
> Thanks a lot!
>
> Mirek
>
> ______________________________________________
> 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

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