R 使用另一个列中的值索引数据框

Question

I have a data frame, and two of the columns are indices for another data fame. I want to add a column to the first by indexing the second, but just calling the column names isn't working. For example, if the first data frame is:

...  Gene    CellLine ...
     KRAS    HELA     ...
     BRCA1   T24      ...

and my second dataframe looks like

        KRAS   BRCA1 ...
HELA    5      3
T24     2      1
...

I want the output to look like

...  Gene   CellLine   Dependency ...
     KRAS   HELA       5          ...
     BRCA1  T24        1          ...

without having to loop through the lines because the first data frame is massive. That is, is there any function or package that would do the equivalent to

for (i in rownames(table1)){
  table1[i, dependency] <- ifelse(table1[i,"Gene"] %in% rownames(table2) & table1[i,"CellLine"] %in% colnames(table2), table2[table1[i,"Gene"],table1[i,"CellLine"]], NA)
}

but faster?

Thanks!

Answer 1

The following code is vectorized, it creates an index matrix with the two columns from df1 and uses it to extract the required values from df2 .

inx <- as.matrix(df1[c("CellLine", "Gene")])
df1$Dependency <- df2[inx]

df1
#   Gene CellLine Dependency
#1  KRAS     HELA          5
#2 BRCA1      T24          1

Data

df1 <- read.table(text = "
Gene    CellLine 
KRAS    HELA
BRCA1   T24 
", header = TRUE)

df2 <- read.table(text = "
        KRAS   BRCA1
HELA    5      3
T24     2      1
", header = TRUE)

Answer 2

You can try this approach. The data used is next:

#Data
df1 <- structure(list(Gene = c("KRAS", "BRCA1"), CellLine = c("HELA", 
"T24")), class = "data.frame", row.names = c(NA, -2L))
df2 <- structure(list(id = c("HELA", "T24"), KRAS = c(5L, 2L), BRCA1 = c(3L, 
1L)), class = "data.frame", row.names = c(NA, -2L))

Then the code, you can melt and merge data:

library(reshape)
#Melt df2 
Melted <- melt(df2,id.vars = 'id')
#Now merge
Merged <- merge(df1,Melted,by.x=c('Gene','CellLine'),by.y=c('variable','id'),all.x=T)

The result would be next:

   Gene CellLine value
1 BRCA1      T24     1
2  KRAS     HELA     5