coalesce

So this is the meat of the question: Can Foo.Bar ever return null? To clarify, can '_bar' be set to null after it's evaluated as non-null and before it's value is returned? public class Foo { Object _bar; public Object Bar { get { return _bar ?? new Object(); } set { _bar = value; } } } I know using the following get method is not safe, and can return a null value: get { return _bar != null ? _bar : new Object(); } UPDATE: Another way to look at the same problem, this example might be more clear: public static T GetValue<T>(ref T value) where T : class, new() { return value ?? new T(); } And

Hell when I do: select COALESCE (CORP_ID, 0) from crmuser.accounts; The CORP_ID records which are Null returns 0 but when I do: select COALESCE (EMAIL, 'NO EMAIL') from crmuser.accounts I get an error: ORA-12704: character set mismatch The EMAIL field in NVARCHAR2(30). Is is My Datatype and if so What should I do to return default Values? you should do select COALESCE (EMAIL, n'NO EMAIL') from crmuser.accounts to convert the literal to NVARCHAR. eg http://sqlfiddle.com/#!4/73929/1 vs http://sqlfiddle.com/#!4/73929/2 This generic fix works with columns defined as either VARCHAR2 or NVARCHAR2:

I know this is a duplicate Q but I can't seem to find the post again Using the following data df <- data.frame(A=c(1,1,2,2),B=c(NA,2,NA,4),C=c(3,NA,NA,5),D=c(NA,2,3,NA),E=c(5,NA,NA,4)) A B C D E 1 NA 3 NA 5 1 2 NA 2 NA 2 NA NA 3 NA 2 4 5 NA 4 Grouping by A , I'd like the following output using a tidyverse solution A B C D E 1 2 3 2 5 2 4 5 3 4 I have many groups in A . I think I saw an answer using coalesce but am unsure how to get it work. I'd like a solution that works with characters as well. Thanks! Not tidyverse but here's one base R solution df <- data.frame(A=c(1,1),B=c(NA,2),C=c(3,NA)

I'm tempted to lie and say that English is my second language, but the truth is that I just have no idea what 'Coalescing' means. I know what ?? 'does' in C#, but the name doesn't make sense to me. I looked up the word and I understand it to be a synonym for 'join'. 'Null Join Operator' still doesn't make sense. Can someone enlighten me? I'm tempted to lie and say that English is my second language...but the truth is that I just have no idea what 'Coalescing' means. I know what ?? 'does' in C#, but the name doesn't make sense to me. I looked up the word and I understand it to be a synonym for

I have a dataframe that has two rows: | code | name | v1 | v2 | v3 | v4 | |------|-------|----|----|----|----| | 345 | Yemen | NA | 2 | 3 | NA | | 346 | Yemen | 4 | NA | NA | 5 | Is there an easy way to merge these two rows? What if I rename "345" in "346", would that make things easier? You can use aggregate . Assuming that you want to merge rows with identical values in column name : aggregate(x=DF[c("v1","v2","v3","v4")], by=list(name=DF$name), min, na.rm = TRUE) name v1 v2 v3 v4 1 Yemen 4 2 3 5 This is like the SQL SELECT name, min(v1) GROUP BY name . The min function is arbitrary, you