R - replace values in data frame using lookup table

问题

I was having some trouble lately trying to replace specific values in a data frame or matrix by using a lookup-table.

So this represents the original.data to be modified ...

    V1  V2  V3  V4  V5  V6  V7  V8  V9 V10 V11 V12 V13 V14
1  255 255 255 255 255 255 255 255 255 255 255 255 255 255
2  255 255 255 255 255 255 255 255   3   3 255 255 255 255
3  255 255 255 255 255   1   3   3   3   3   3 255 255 255
4  255 255   5   5   5   1   3   3   4   4   3 255 255 255
5  255   5   5   5   5   1   3   4   4   4   4 255 255 255
6  255   5   5   5   1   3   3   3   4   4   3   3 255 255
7  255 255   5   1   3   3   3   3   6   6   6   3 255 255
8  255 255   1   1   1   1   2   2   3   3   6   3 255 255
9  255 255   1   1   1   2   2   2   2   2   3   3   3 255
10 255 255 255   1   2   2   2   2   2   2   2   3   3 255
11 255 255 255   2   2   2   2   2   7   7   7   2 255 255
12 255 255 255   2   2   8   8   8   7 255 255 255 255 255
13 255 255 255 255   8   8 255 255 255 255 255 255 255 255
14 255 255 255 255 255 255 255 255 255 255 255 255 255 255

... and following may be the lookup.table (rows=1:9, column1="Sub", column2="Main"):

  Sub Main
1   1    1
2   2    2
3   3    3
4   4    4
5   5    5
6 255  255
7   6    3
8   7    2
9   8    2

The aim is to compare e.g. original.data[11,11] [7] with lookup.tabel[8,"Sub"] [7]

... and write a new matrix modified.data[11,11] with lookup.table[8,"Main"] [2]. Until now all I came up with is using for-loops and an if-statement,

for (i in 1:ncol(original.data)){
  for (j in 1:nrow(lookup.table)){
    if (original.data[i,i]==lookup.table[j,1]){
      origingal.data[j,i]<-lookup.table[j,2]
    }
  }
}

which leads to

Error in origingal.data[j, i] <- lookup.table[j, 2] : 
  object 'origingal.data' not found

but i cannot figure out my errors in reasoning.

I'd love to get some hints.

Thanks

\\\\\PROBLEM SOLVED

for (i in 1:ncol(original.data)){
  for (j in 1:nrow(original.data)){
    for (x in 1:nrow(lookup.table)){
      if (original.data[j,i]==lookup.table[x,1]){
        original.data[j,i]<-lookup.table[x,2]
      }
    } 
  }
}

... works, but this is a much faster method:

for(i in 1:nrow(lookup.table)){
  c<-lookup.table[b,2]
  d<-lookup.table[b,3]
  original.data_modified[original.data == c] <- d
}

回答1:

you can try :

# x the original.data (a matrix)
# y the lookup.table
x2 <- y[match(x, y[,1]),2]
dim(x2) <- dim(x)
table(x, x2)
     x2
x       1   2   3   4   5 255
  1    13   0   0   0   0   0
  2     0  22   0   0   0   0
  3     0   0  29   0   0   0
  4     0   0   0   8   0   0
  5     0   0   0   0  11   0
  6     0   0   4   0   0   0
  7     0   4   0   0   0   0
  8     0   5   0   0   0   0
  255   0   0   0   0   0 100

来源：https://stackoverflow.com/questions/22475400/r-replace-values-in-data-frame-using-lookup-table