[英]Extract values from data frame using data frame of indexes - R
I have a data frame of useful information: 我有一个有用信息的数据框:
X = c(1,2,3,4,5,6,7,8,9,10)
Y = c(5,4,3,2,1,0,1,2,3,4)
Z = c(11,12,13,14,15,16,17,18,19,20)
df <- data.frame(X, Y, Z)
And a data frame of row and column positions: 以及行和列位置的数据框:
row <- c(6,2,5)
column <- c(1,2,3)
pos <- data.frame(row, column)
I would like to use some function ( fun
) that uses the column and row positions in pos
to return the values in df
occupying those positions, eg 我想使用一些函数(
fun
),该函数使用pos
的列和行位置来返回df
占据这些位置的值,例如
fun(df, pos$row, pos$column)
[1] 6 4 15
I thought I could do it like this, but to no avail 我以为我可以这样做,但无济于事
df[c(pos$row),c(pos$col)]
The row/column index works as a matrix
, so we convert to the 'pos' to a matrix
and use that as row/column index for extracting the values. 行/列索引用作
matrix
,因此我们将'pos'转换为matrix
并将其用作行/列索引以提取值。
df[as.matrix(pos)]
or otherwise, cbind
the columns of 'pos' as cbind
of vector
s returns a matrix
或以其它方式,
cbind
的“POS”的列作为cbind
的vector
小号返回一个matrix
df[cbind(pos$row, pos$column)]
This can be converted to a function 可以转换成函数
fExtract <- function(dat, indexDat){
dat[as.matrix(indexDat)]
}
fExtract(df, pos)
#[1] 6 4 15
You could also do this with a function inside a call to sapply
, working down the rows of pos
: 您也可以通过调用
sapply
内的函数来完成此sapply
,从而处理pos
的行:
sapply(seq(nrow(pos)), function(i) df[pos$row[i], pos$column[i]])
[1] 6 4 15
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