# [R] request: How to get column name

Chuck Cleland ccleland at optonline.net
Wed Sep 3 17:34:24 CEST 2008

```On 9/3/2008 11:05 AM, Petr PIKAL wrote:
> r-help-bounces at r-project.org napsal dne 03.09.2008 15:54:08:
>
>> try this:
>>
>> x <- c(3,3,3,3,0,0,0,0,5,5,5,5,8,8,8,8)
>> x <- matrix(x, nrow=4)
>>
>> which(colSums(x == 0) == nrow(x))
>
> Isn't this the same?
>
> which(colSums(x)==0)

No, because the column sum can be zero without each element being zero:

x <- c(3,3,3,3,1,-1,1,-1,5,5,5,5,8,8,8,8)
x <- matrix(x, nrow=4)

> which(colSums(x == 0) == nrow(x))
integer(0)

> which(colSums(x)==0)
[1] 2

> Regards
> Petr
>
>> I hope it helps.
>>
>> Best,
>> Dimitris
>>
>>
>>> Dear R community
>>> I have a problem regarding which of the column in a matrix contains
> all of
>> zero elements. e.g.
>>> x=c(3,3,3,3,0,0,0,0,5,5,5,5,8,8,8,8); x=matrix(x, nrow=4)
>>> the output is
>>>
>>>> x
>>>>
>>>      [,1] [,2] [,3] [,4]
>>> [1,]    3    0    5    8
>>> [2,]    3    0    5    8
>>> [3,]    3    0    5    8
>>> [4,]    3    0    5    8
>>> In this case the required column is second so the result should be
> "2". How
>> can i get it?
>>>
>>> best regards
>>>
>>>
>>>
>>>
>>>
>>>    [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>>
>>
>> --
>> Dimitris Rizopoulos
>> Assistant Professor
>> Department of Biostatistics
>> Erasmus University Medical Center
>>
>> Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
>> Tel: +31/(0)10/7043399
>> Fax: +31/(0)10/7044657
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
> 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
> and provide commented, minimal, self-contained, reproducible code.
>

--
Chuck Cleland, Ph.D.
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```