[R] if condition doesn't evaluate to True/False

[ml-r-help at epigenomics.com]

Petr PIKAL wrote:
> Hi
> 
> r-help-bounces at r-project.org napsal dne 29.04.2009 17:05:01:
> 
>> see
>> ?is.null
>>
>> e.g.
>> if( is.null(sub_grp_whr_cls_data[sbgrp_no, 1]) )
>> {
>>   your code
>> }
> 
> It probably will not work as 
> 
> sub_grp_whr_cls_data[sbgrp_no,1]=="NULL"
> 
> implicates that there is character value "NULL". I am not sure if you can 
> get NULL as a part of some object. I tried and failed.
> See what you get
> x<- c(1,2,3, NULL)
> 
> Regards
> Petr

thanks for pointing this out clearly, I had thought only about making the comparison
return a logical for use in the expression.

On hindsight it seems implausible to ever get NULL in the matrix/data frame.

(DONT USE
playing around I found the following abuse to work
m <- as.data.frame(diag(3))
m[[3]][3] <- list(NULL)
is.null(m[3,3][[1]])
[1] TRUE
)
Regards,
  Matthias

> 
>> Moumita Das wrote:
>>> Hi friends,
>>> Please help me with this bug.
>>>
>>> *Bug in my code:*
>>>
>>> In this variable sub_grp_whr_cls_data[sbgrp_no,1] I store the where
>>> clause.every sub group has a where condition linked with it.
>>>
>>> Database1
>>>
>>>
>>> Where clause  was  not found for a particular subgroup,
>>> sub_grp_whr_cls_data[sbgrp_no,1]  value was NULL
>>>
>>> So the condition (*sub_grp_whr_cls_data[sbgrp_no,1]=="NULL" ||
>>> sub_grp_whr_cls_data[sbgrp_no,1]==""*) should evaluate to TRUE ,but it
>>> evaluated to NA
>>>
>>> So the if block where I used the the condition threw error
>>>
>>> If(*sub_grp_whr_cls_data[sbgrp_no,1]=="NULL" ||
>>> sub_grp_whr_cls_data[sbgrp_no,1]==""*)
>>>
>>> i.e if(NA)
>>>
>>> Error:--
>>>
>>> Error in if (sub_grp_whr_cls_data[sbgrp_no, 1] == "NULL" ||
>>> sub_grp_whr_cls_data[sbgrp_no,  :
>>>
>>>   missing value where TRUE/FALSE needed
>>>
>>> Comments:-- but when there ‘s no where clause value the condition
>>> (sub_grp_whr_cls_data[sbgrp_no,1]=="NULL"
>>> ||sub_grp_whr_cls_data[sbgrp_no,1]=="") should automatically evaluate 
> to *
>>> TRUE*
>>>
>>>
>>>
>>> Database2
>>>
>>> Where clause  was  found for a particular subgroup
>>>
>>> The condition (sub_grp_whr_cls_data[sbgrp_no,1]=="NULL"
>>> ||sub_grp_whr_cls_data[sbgrp_no,1]=="") evaluated to FALSE
>>>
>>> So if (sub_grp_whr_cls_data[sbgrp_no,1]=="NULL"
>>> ||sub_grp_whr_cls_data[sbgrp_no,1]=="") is
>>>
>>> If (FALSE) ,control goes to the else part.
>>>
>>> This is exactly what is expected of the program.
>>>
>>> *QUERY:-- **If the condition evaluates to FALSE  when a where 
> condition is
>>> available why doesn’t it evaluate to TRUE when a where condition 
> available
>>> is NULL or no where condition is available.*
>>>
>>> Here I have taken the example of two databases where I tried to get 
> the
>>> where clause for subgroup 1.In case of Database1 it was not available 
> in
>>> case of Databse2 it was available.But the problem may appear for the 
> same
>>> database also, when where clause is available for say one subgroup and 
> not
>>> for the other.
>>>
>>>
>>>
>>>
> ------------------------------------------------------------------------
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>>
>> -- 
>> Matthias Burger                     Project Manager/ Biostatistician
>> Epigenomics AG    Kleine Praesidentenstr. 1    10178 Berlin, Germany
>> phone:+49-30-24345-0                            fax:+49-30-24345-555
>> http://www.epigenomics.com           matthias.burger at epigenomics.com
>> --
>> Epigenomics AG Berlin           Amtsgericht Charlottenburg HRB 75861
>> Vorstand:                           Geert Nygaard (CEO/Vorsitzender)
>>                                             Oliver Schacht PhD (CFO)
>> Aufsichtsrat:   Prof. Dr. Dr. hc. Rolf Krebs (Chairman/Vorsitzender)
>>
>> ______________________________________________
>> 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.
> 
> ______________________________________________
> 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.


-- 
Matthias Burger                     Project Manager/ Biostatistician
Epigenomics AG    Kleine Praesidentenstr. 1    10178 Berlin, Germany
phone:+49-30-24345-0                            fax:+49-30-24345-555
http://www.epigenomics.com           matthias.burger at epigenomics.com
--
Epigenomics AG Berlin           Amtsgericht Charlottenburg HRB 75861
Vorstand:                           Geert Nygaard (CEO/Vorsitzender)
                                            Oliver Schacht PhD (CFO)
Aufsichtsrat:   Prof. Dr. Dr. hc. Rolf Krebs (Chairman/Vorsitzender)