R help - Apr 2009 - if condition doesn't evaluate to True/False

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.

-- 
Thanks
Moumita

	[[alternative HTML version deleted]]

see
?is.null

e.g.
if( is.null(sub_grp_whr_cls_data[sbgrp_no, 1]) )
{
  your code
}

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.
> 
> 
> 
> ------------------------------------------------------------------------
> 
> ______________________________________________
> 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)

Hi

you put your problem in absolutely messy state

r-help-bounces at r-project.org napsal dne 29.04.2009 16:16:55:
> 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
Are you sure that 
sub_grp_whr_cls_data[sbgrp_no,1] was either "NULL" or ""

I suspect that it is NA

you can get three results with logical values
> x<-c(1,"NULL", NA, "", 1)
> x=="NULL"|x==""
[1] FALSE  TRUE    NA  TRUE FALSE

So if the value is "NULL" or "" you will get TRUE, if it is
anything else
you will get FALSE but if it is NA you will get NA.

Actually if the value is NA you do not know if it should be "NULL",
"" or
anything else therefore result is NA

Regards
Petr
> 
> 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.
> 
> -- 
> Thanks
> Moumita
> 
>    [[alternative HTML version deleted]]
> 
> ______________________________________________
> 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.