[R] Argh! Trouble using string data read from a file

jim holtman jholtman at gmail.com
Thu Oct 16 02:09:30 CEST 2008 

You have to explicitly 'print' the value of x in the loop:    print(x)

'x' by itself is just it value.  At the command line, typing an
objects name is equivalent to printing that object, but it only
happens at the command line.  If you want a value printed, the 'print'
it.  Also works at the command line if you want to use it there also.

On Wed, Oct 15, 2008 at 5:36 PM, Ted Byers <r.ted.byers at gmail.com> wrote:
> Actually, I'd tried single brackets first.  Here is what I got:
>
>> for (i in 1:length(V4) ) { x = read.csv(V4[i], header = FALSE, na.strings="");x }
> Error in read.table(file = file, header = header, sep = sep, quote = quote,  :
>  'file' must be a character string or connection
>>
>
>
> the advice to use as.character worked, in that progress has been made.
>
> Can you guys explain the following output, though?
>
>> setwd("K:\\MerchantData\\RiskModel\\AutomatedRiskModel")
>> for (i in 1:length(V4) ) { x = read.csv(as.character(V4[[i]]), header = FALSE, na.strings="");x }
>> x
>  V1
> 1  0
>> x = read.csv(as.character(V4[[1]]), header = FALSE, na.strings="");x
>     V1
> 1     0
> 2     0
> 3    21
> 4     0
> 5     1
> 6     7
> 7    51
> 8    20
> 9     3
> 10    5
> 11    6
> 12    8
> 13    2
> 14    0
> 15    2
> 16    4
> 17   23
>
> Clearly, if I hand write a line to read the data, getting the file
> name from V4 (in this case V4[[1]]), I get the data into 'x', which I
> can then display.  I only displayed the first few as some of these
> files will have thousands of values.
>
> But what puzzles me is that I saw virtually no output from my loop.  I
> thought what would happen (with the x after the ';') is that the
> contents of each file would be displayed after it is read and before
> the first is read.  And after the loop finishes, there is nothing in
> x.  I don't see why the contents of x would disappear after the loop,
> unless R has scoping restrictions as stringent as, say, C++ (e.g. a
> variable declared inside a loop is not visible outside the loop).  But
> that would beg the question as to how to declare a variable before it
> is first used.
>
> This doesn't bode well for me, or perhaps my ability to learn a new
> trick at my age, when such a simple loop should give me such trouble.
> :-(
>
> Getting more grey hair by the minute.  :-(
>
> Thanks
>
> ted
>
> On Wed, Oct 15, 2008 at 5:12 PM, Rolf Turner <r.turner at auckland.ac.nz> wrote:
>>
>> On 16/10/2008, at 10:03 AM, jim holtman wrote:
>>
>>> try putting as.character in the call:
>>>
>>> x = read.csv(as.character(V4[[i]]), header = FALSE
>>
>> No.  This won't help.  V4 is a column of the data frame optdata,
>> and hence is a vector.  Not a list!  Use single brackets --- V4[i] ---
>> and all will be well.
>>
>>        cheers,
>>
>>                Rolf
>>>
>>> On Wed, Oct 15, 2008 at 4:46 PM, Ted Byers <r.ted.byers at gmail.com> wrote:
>>>>
>>>> Here is what I tried:
>>>>
>>>> optdata =
>>>> read.csv("K:\\MerchantData\\RiskModel\\AutomatedRiskModel\\soptions.dat",
>>>> header = FALSE, na.strings="")
>>>> optdata
>>>> attach(optdata)
>>>> for (i in 1:length(V4) ) { x = read.csv(V4[[i]], header = FALSE,
>>>> na.strings="");x }
>>>>
>>>> And here  is the outcome (just a few of the 60 records successfully
>>>> read):
>>>>>
>>>>> optdata =
>>>>>
>>>>> read.csv("K:\\MerchantData\\RiskModel\\AutomatedRiskModel\\soptions.dat",
>>>>> header = FALSE, na.strings="")
>>>>> optdata
>>>>
>>>>   V1   V2 V3                        V4
>>>> 1  251 2008 18 Plus_Shipping.2008.18.dat
>>>> 2  251 2008 19 Plus_Shipping.2008.19.dat
>>>> 3  251 2008 20 Plus_Shipping.2008.20.dat
>>>> 4  251 2008 22 Plus_Shipping.2008.22.dat
>>>> 5  251 2008 23 Plus_Shipping.2008.23.dat
>>>> 6  251 2008 24 Plus_Shipping.2008.24.dat
>>>>
>>>> I can see the data has been correctly read.  But for some reason that
>>>> isn't
>>>> clear, read.csv doesn't like the data in the last column.
>>>>
>>>>> attach(optdata)
>>>>> for (i in 1:length(V4) ) { x = read.csv(V4[[i]], header = FALSE,
>>>>> na.strings="");x }
>>>>
>>>> Error in read.table(file = file, header = header, sep = sep, quote =
>>>> quote,
>>>> :
>>>>  'file' must be a character string or connection
>>>>>
>>>>> V4[[1]]
>>>>
>>>> [1] Plus_Shipping.2008.18.dat
>>>> 60 Levels: Easyway.2008.17.dat Easyway.2008.18.dat Easyway.2008.19.dat
>>>> Easyway.2008.20.dat ... Secured_Pay.2008.31.dat
>>>>
>>>>>
>>>>
>>>> The last column is comprised of valid Windows filenames (and no
>>>> whitespace,
>>>> so as not to confuse things).
>>>>
>>>> I see in the docuentation "`[[...]]' is the operator used to select a
>>>> single
>>>> element, whereas `[...]' is a general subscripting operator.", so I
>>>> assume
>>>> V4[[i]] is the correct way to get the ith value from V4.  So why does
>>>> read.csv complain that "'file' must be a character string or connection"?
>>>> It seems obvious that the value in V4[[i]i] is a string.  V4[[1]] does
>>>> give
>>>> me the right value, although that is followed by output I didn't ask for.
>>>>
>>>> In the loop above, I was going to replace the output obtained by 'x' with
>>>> output from fitdistr(x,"exponential"), but I can't proceed with that
>>>> until I
>>>> can get the data in these files read.
>>>>
>>>> What have I missed?
>>>>
>>>> Thanks
>>>>
>>>> Ted
>>>> --
>>>> View this message in context:
>>>> http://www.nabble.com/Argh%21--Trouble-using-string-data-read-from-a-file-tp20002064p20002064.html
>>>> Sent from the R help mailing list archive at Nabble.com.
>>>>
>>>> ______________________________________________
>>>> 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
>>>
>>> What is the problem that you are trying to solve?
>>>
>>> ______________________________________________
>>> 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.
>>
>>
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>
> ______________________________________________
> 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

What is the problem that you are trying to solve?

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