[R] help with dealing with integer(0) returns from grep used within a conditional loop

[Duncan Murdoch]

On 04/07/2009 6:09 PM, Henrique Dallazuanna wrote:
> You cas use isTRUE:
> 
> isTRUE(grep("a", "bbbb") > 0)

Not really.  If there are multiple hits, that returns FALSE.

You want to use length(grep(...)) to detect any hits.

Duncan Murdoch


> 
> 
> On Sat, Jul 4, 2009 at 2:56 PM, Mark Kimpel <mwkimpel at gmail.com> wrote:
> 
>> I am using grep to locate colnames to automate a report build and have
>> run into a problem when a colname is not found. The use of integer(0)
>> in a conditional statement seems to be a no no as it has length 0.
>> Below is a self-contained trivial example. I would like to get
>> something like "NA" or -1 for the position when it is not found OR
>> learn a way to use integer(0) or some "cast" of it in a logical
>> statement. Example, output, and sessionInfo follow. Thanks, Mark
>>
>> ####################################3
>> vec.1 <- c("a", "b", "c")
>> vec.2 <- c("a", "c", "d")
>> for (i in 1:length(vec.1)){
>>  for (j in 1:length(vec.2)){
>>    print(paste("i:", i, " j:", j, sep = ""))
>>    pos <- grep(vec.1[i], vec.2[j])
>>    if (pos > 0){
>>      print("pos identified")
>>    }
>>    else{
>>      print("pos not found")
>>    }
>>  }
>> }
>> ################################
>>
>>> #################################3
>>> vec.1 <- c("a", "b", "c")
>>> vec.2 <- c("a", "c", "d")
>>> for (i in 1:length(vec.1)){
>> +   for (j in 1:length(vec.2)){
>> +     print(paste("i:", i, " j:", j, sep = ""))
>> +     pos <- grep(vec.1[i], vec.2[j])
>> +     if (pos > 0){
>> +       print("pos identified")
>> +     }
>> +     else{
>> +       print("pos not found")
>> +     }
>> +   }
>> + }
>> [1] "i:1 j:1"
>> [1] "pos identified"
>> [1] "i:1 j:2"
>> Error in if (pos > 0) { : argument is of length zero
>> No suitable frames for recover()
>>> ###############
>>> sessionInfo()
>> R version 2.9.1 (2009-06-26)
>> x86_64-unknown-linux-gnu
>>
>> locale:
>>
>> LC_CTYPE=en_US.UTF-8;LC_NUMERIC=C;LC_TIME=en_US.UTF-8;LC_COLLATE=en_US.UTF-8;LC_MONETARY=C;LC_MESSAGES=en_US.UTF-8;LC_PAPER=en_US.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US.UTF-8;LC_IDENTIFICATION=C
>>
>> attached base packages:
>> [1] tcltk     stats     graphics  grDevices datasets  utils     methods
>> [8] base
>>
>> other attached packages:
>>  [1] sfsmisc_1.0-7       KEGG.db_2.2.11      GO.db_2.2.11
>>  [4] rat2302.db_2.2.11   GOstats_2.10.0      RSQLite_0.7-1
>>  [7] DBI_0.2-4           graph_1.22.2        Category_2.10.1
>> [10] AnnotationDbi_1.6.1 qvalue_1.18.0       limma_2.18.2
>> [13] affy_1.22.0         Biobase_2.4.1
>>
>> loaded via a namespace (and not attached):
>>  [1] affyio_1.12.0        annotate_1.22.0      genefilter_1.24.2
>>  [4] GSEABase_1.6.1       preprocessCore_1.6.0 RBGL_1.20.0
>>  [7] splines_2.9.1        survival_2.35-4      tools_2.9.1
>> [10] XML_2.5-3            xtable_1.5-5
>> ------------------------------------------------------------
>> Mark W. Kimpel MD  ** Neuroinformatics ** Dept. of Psychiatry
>> Indiana University School of Medicine
>>
>> 15032 Hunter Court, Westfield, IN  46074
>>
>> (317) 490-5129 Work, & Mobile & VoiceMail
>>
>> "The real problem is not whether machines think but whether men do."
>> -- B. F. Skinner
>>
>> ______________________________________________
>> 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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