[R] editing a data.frame

[john.polo]

Daniel Folkinshteyn wrote:
> works for me:
> > sub('1.00', '1', '1.00E-20')
> [1] "1E-20"
when i input what you wrote, i get the same result. but that doesn't 
change the value for TreeTag at row 1501, it's just floating around in 
space. if i try it for yr1bp$TreeTag[1501], which is 1.00E-20 i get this:

 > yr1bp$TreeTag[1501]<-sub("1.00", "1", yr1bp$TreeTag[1501])
Warning message:
In `[<-.factor`(`*tmp*`, 1501, value = "1E-20") :
  invalid factor level, NAs generated

and then 1501 turns into:
1501    <NA>   2001 adult 32.5

which is less useful than the way it was originally input. thanks for 
the suggestion.

john

> finally, if all your target strings are of the form 1.00E-20, you 
> could sub the whole thing with a more general regexp:
>
> sub("([0-9])(\.[0-9]{2})(.*)", "\\1\\3", yourvector)
> (it matches a digit, followed by a dot and two digits, followed by 
> "anything else", and takes out the "dot and two digits" bit in the 
> replacement, in the whole vector.)
thanks for that suggestion. it could come in handy.


> on 06/06/2008 03:25 PM john.polo said the following:
>> dear R users,
>>
>> the data frame (read in from a csv) looks like this:
>>        TreeTag     Census    Stage     DBH
>> 1     CW-W740   2001 juvenile     5.8
>> 2     CW-W739   2001 juvenile     4.3
>> 3     CW-W738   2001 juvenile     4.7
>> 4     CW-W737   2001 juvenile     5.4
>> 5     CW-W736   2001 juvenile     7.4
>> 6     CW-W735   2001 juvenile     5.4
>> ...
>> 1501 1.00E-20   2001  adult      32.5
>>
>> i would like to change values under the TreeTag column. as the last 
>> value shows, some of the tags have decimals followed by 2 decimal 
>> places. i just want whole numbers, i.e. not 1.00E-20, but 1E-20. i 
>> have a rough understanding of regexp and grepped all the positions 
>> that have the inappropriate tags. i tried sub() a couple of different 
>> ways, like
>> yr1bp$TreeTag[1501]<-sub("1.00", "1", yr1bp$TreeTag[1501])
>> and after turning yr1bp$TreeTag[1501] into <NA>,
>> yr1bp$TreeTag[1501]<-sub("", "1E-20", yr1pb$TreeTag[1501])
>> and
>> sub("", "1E-20", yr1bp$TreeTag[1501])
>> but it's not working. i guess it has something to do with the 
>> data.frame characteristics i'm not aware of or don't understand. 
>> would i somehow have to tear apart the columns, edit them, and then 
>> put it back together? not that i know how to do that, but i'm 
>> wondering out loud.
>>
>> john
>>
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