CODEWITHSUNDEEP
rreplacedataframe
user3093050
user3093050

Reputation: 13

how to replace values in every nth column with value from adjoining column

I have a data frame (m2) with 1127 columns and 314 rows. Starting at column 1, I need to replace the values in every 5th column with the 1st value in the adjoining column. I have been able to do this for individual columns selecting by column name as here: 

m2$Col1<-m2[1,2]
m2$Col6<-m2[1,7]
m2$Col11<-m2[1,12]

or by a very clunky reassign/recombine:

newcol1<-replace(m2[,1],1:314,m2[1,2])
m2<-cbind(newcol1,m2[,2:1127])
newcol2<-replace(m2[,6],1:314,m2[1,7])
m2<-cbind(m2[,1:5],newcol2,m2[,7:1127])
newcol3<-replace(m2[,11],1:314,m2[1,12])
m2<-cbind(m2[,1:10],newcol3,m2[,12:1127])

I am hoping to find a way to automate this for the data frame. I am not yet literate in for loops. Can something like this be done with a function?

Upvotes: 1

Views: 1501

Answers (2)

IRTFM
IRTFM

Reputation: 263301

Initial thought;

m2[, c(TRUE, rep(FALSE,4) )] <- m2[ , c(FALSE, TRUE, FALSE,FALSE,FALSE) ]

That was thinking this was a column-for-column replacement, but re-reading the question, it appears not;

Perhaps:

m2[, c(TRUE, rep(FALSE,4) )] <- rep( m2[1 , c(FALSE, TRUE, FALSE,FALSE,FALSE) ], each=nrow(m2) )

But that was it either and it needed an unlist operation to provide a tested solution:

 m2 <- as.data.frame(matrix(1:150, nrow=10))  
m2[, c(TRUE, rep(FALSE,4) )] <- 
                  unlist(rep( m2[ 1, c(FALSE, TRUE, FALSE,FALSE,FALSE) ], each=nrow(m2) ))
> m2
   V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15
1  11 11 21 31 41 61 61 71 81  91 111 111 121 131 141
2  11 12 22 32 42 61 62 72 82  92 111 112 122 132 142
3  11 13 23 33 43 61 63 73 83  93 111 113 123 133 143
4  11 14 24 34 44 61 64 74 84  94 111 114 124 134 144
5  11 15 25 35 45 61 65 75 85  95 111 115 125 135 145
6  11 16 26 36 46 61 66 76 86  96 111 116 126 136 146
7  11 17 27 37 47 61 67 77 87  97 111 117 127 137 147
8  11 18 28 38 48 61 68 78 88  98 111 118 128 138 148
9  11 19 29 39 49 61 69 79 89  99 111 119 129 139 149
10 11 20 30 40 50 61 70 80 90 100 111 120 130 140 150

Upvotes: 0

Stephen Henderson
Stephen Henderson

Reputation: 6522

It's difficult without the actual data to check but I think you mean:

  #all the fifth cols
  fifth= seq(1, ncol(m), 5)
  # and the adjacent
  adj= fifth+1

  m[,fifth]= m[1,adj]

NB this doesn't check for correctness of your columns i.e. that there is an adjacent column. I just assume from your description there is.

Upvotes: 2

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