# [R] Replacing value with "1"

Richard M. Heiberger rmh at temple.edu
Fri Sep 30 06:32:43 CEST 2016

```I got the matrix time down by another factor of 4

tmp <- matrix(c(0,0,1,0,0,
NA,0,1,1,0,
0,1,0,0,NA,
1,0,1,0,1), ## last item in row has value 1
byrow=TRUE, 4, 5)

## Jeff matrix
DF2 <- DF <- tmp
DF2[ , -1 ] <- ifelse(   !is.na( DF[ , -ncol( DF ) ] )
& 1 == DF[ , -ncol( DF ) ]
, 1
, DF[ , -1 ]
)
DF2
##
system.time( for (i in 1:1000) {
DF2[ , -1 ] <- ifelse(   !is.na( DF[ , -ncol( DF ) ] )
& 1 == DF[ , -ncol( DF ) ]
, 1
, DF[ , -1 ]
)
})
##   user  system elapsed
##  0.027   0.001   0.029

## rmh matrix
DF <- tmp
DF[,-1][(DF[,-ncol(DF)] == 1)] <- 1
DF
##
system.time( for (i in 1:1000) {
DF[,-1][(DF[,-ncol(DF)] == 1)] <- 1
})
##   user  system elapsed
##  0.007   0.000   0.006

On Fri, Sep 23, 2016 at 12:25 PM, Jeff Newmiller
<jdnewmil at dcn.davis.ca.us> wrote:
> Another approach using in-place replacement and thinking with matrix
> operations instead of vector operations:
>
> DF <- matrix( c( 0,  0, 1, 0, 0
>                , NA, 0, 1, 1, 0
>                , 0,  1, 0, 0, NA )
>             , byrow=TRUE
>             , nrow=3 )
> DF2 <- DF
> DF2[ , -1 ] <- ifelse(   !is.na( DF[ , -ncol( DF ) ] )
>                        & 1 == DF[ , -ncol( DF ) ]
>                      , 1
>                      , DF[ , -1 ]
>                      )
>
>
> On Thu, 22 Sep 2016, Henrik Bengtsson wrote:
>
>> which(df == 1, arr.ind=TRUE) is useful here:
>>
>>> df <- matrix(c(0,NA,0,0,0,1,1,1,0,0,1,0,0,0,NA), nrow=3)
>>> df
>>
>>     [,1] [,2] [,3] [,4] [,5]
>> [1,]    0    0    1    0    0
>> [2,]   NA    0    1    1    0
>> [3,]    0    1    0    0   NA
>>
>>> ## Identify (row,col) indices for 1:s
>>> idxs <- which(df == 1, arr.ind=TRUE)
>>> idxs
>>
>>     row col
>> [1,]   3   2
>> [2,]   1   3
>> [3,]   2   3
>> [4,]   2   4
>>
>>> ## Drop any in the last column
>>> idxs <- idxs[idxs[,"col"] < ncol(df), , drop=FALSE]
>>> idxs
>>
>>     row col
>> [1,]   3   2
>> [2,]   1   3
>> [3,]   2   3
>> [4,]   2   4
>>
>>> idxs[,"col"] <- idxs[,"col"] + 1L
>>> idxs
>>
>>     row col
>> [1,]   3   3
>> [2,]   1   4
>> [3,]   2   4
>> [4,]   2   5
>>
>>> df[idxs] <- 1
>>> df
>>
>>     [,1] [,2] [,3] [,4] [,5]
>> [1,]    0    0    1    1    0
>> [2,]   NA    0    1    1    1
>> [3,]    0    1    1    0   NA
>>
>> /Henrik
>>
>> On Thu, Sep 22, 2016 at 8:13 PM, Jim Lemon <drjimlemon at gmail.com> wrote:
>>>
>>> Hi Saba,
>>> Try this:
>>>
>>> df<-matrix(c(0,NA,0,0,0,1,1,1,0,0,1,0,0,0,NA),nrow=3)
>>> dimdf<-dim(df)
>>> df1<-df==1
>>> df[cbind(rep(FALSE,dimdf[1]),df1[,-dimdf[2]])]<-1
>>>
>>> Jim
>>>
>>>
>>>
>>> On Fri, Sep 23, 2016 at 12:27 PM, Saba Sehrish via R-help
>>> <r-help at r-project.org> wrote:
>>>>
>>>> Hi
>>>>
>>>> I have a matrix that contains 1565 rows and 132 columns. All the
>>>> observations are either "0" or "1". Now I want to keep all the observations
>>>> same but just one change, i.e. whenever there is "1", the very next value in
>>>> the same row should become "1". Please see below as a sample:
>>>>
>>>>> df
>>>>
>>>>
>>>>      0    0    1    0    0
>>>>     NA    0    1    1    0
>>>>      0    1    0    0    NA
>>>>
>>>> What I want is:
>>>>
>>>>
>>>>     0    0    1    1    0
>>>>    NA    0    1    1    1
>>>>     0    1    1    0    NA
>>>>
>>>>
>>>>
>>>> I shall be thankful for the reply.
>>>>
>>>>
>>>> Saba
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>>> 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 -- To UNSUBSCRIBE and more, see
>>> 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 -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
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