[R] remove rows of a matrix by part of its row name

[William Dunlap]

I think it is simpler to use !grepl() instead of -grep() here, since
subscripting with logicals works properly when there are no matches.
Also, since mat is a matrix, add the argument drop=FALSE so the
result is a matrix when all but one rows are omitted.  E.g.,

> mat <- matrix(1:6, nrow=3, ncol=2,
dimnames=list(c("One","Two","Three"),c("A","B")))
> str(mat[ -grep("T", rownames(mat)), ]) # bad, not a matrix if only one
row wanted
 Named int [1:2] 1 4
 - attr(*, "names")= chr [1:2] "A" "B"
> str(mat[ -grep("X", rownames(mat)), ]) # bad, zero-row matrix if no
unwanted rows
 int[0 , 1:2]
 - attr(*, "dimnames")=List of 2
  ..$ : NULL
  ..$ : chr [1:2] "A" "B"
> str(mat[ !grepl("T", rownames(mat)), , drop=FALSE]) # good, one row
matrix if only one row wanted
 int [1, 1:2] 1 4
 - attr(*, "dimnames")=List of 2
  ..$ : chr "One"
  ..$ : chr [1:2] "A" "B"
> str(mat[ !grepl("X", rownames(mat)), , drop=FALSE]) # good, entire matrix
is no unwanted rows
 int [1:3, 1:2] 1 2 3 4 5 6
 - attr(*, "dimnames")=List of 2
  ..$ : chr [1:3] "One" "Two" "Three"
  ..$ : chr [1:2] "A" "B"



Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, May 22, 2018 at 4:34 AM, Rui Barradas <ruipbarradas using sapo.pt> wrote:

> Hello,
>
> Use grep to get the row indices and then subset with a *negative* index to
> remove those rows.
>
> rn <- scan(what = character(), text = "
> 70/556
> 71.1/280
> 72.1/556
> 72.1/343
> 73.1/390
> 73.1/556
> ")
>
> mat <- matrix(rnorm(6*6), nrow = 6)
> row.names(mat) <- rn
>
> inx <- grep("73\\.", row.names(mat))
>
> new_mat <- mat[-inx, ]
> new_mat
>
>
> Hope this helps,
>
> Rui Barradas
>
>
> On 5/22/2018 11:48 AM, Ahmed Serag wrote:
>
>> Dear R-experts,
>>
>>
>> How can I remove a certain feature or observation by a part of its name.
>> To be clear, I have a matrix with 766 observations as a rows. The row names
>> are like this
>>
>> 70/556
>> 71.1/280
>> 72.1/556
>> 72.1/343
>> 73.1/390
>> 73.1/556
>> Now I would like to remove all the rows that contain the text 73.1
>>
>> Any ideas or suggestion please ?
>>
>>
>> Regards
>>
>>
>>
>>
>> **********************
>>
>> Ahmed Serag
>>
>> Analytical Chemistry Department
>>
>> Faculty of Pharmacy
>>
>> Al-Azhar University
>>
>> Cairo
>>
>> Egypt
>>
>>         [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posti
>> ng-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posti
> ng-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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