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

[ml-r-help at epigenomics.com]

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.
> 
> 
> 
> ------------------------------------------------------------------------
> 
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