我有一个 R x C 矩阵填充到第 k 行并在该行下方为空。我需要做的是填充剩余的行。为了做到这一点,我有一个函数,它接受 2 个整行作为参数,处理这些行并输出 2 个新行(这些输出将填充矩阵的空行,分批 2)。我有一个固定矩阵,其中包含要处理的所有“对”行,但我的 for 循环对性能没有帮助:
# the processRows function:
processRows = function(r1, r2)
{
# just change a little bit the two rows and return it in a compact way
nr1 = r1 * 0.1
nr2 = -r2 * 0.1
matrix (c(nr1, nr2), ncol = 2)
}
# M is the matrix
# nrow(M) and k are even, so nLeft is even
M = matrix(1:48, ncol = 3)
# half to fill (can be more or less, but k is always even)
k = nrow(M)/2
# simulate empty rows to be filled
M[-(1:k), ] = 0
cat('before fill')
print(M)
# number of empty rows to fill
nLeft = nrow(M) - k
nextRow = k + 1
# each row in idxList represents a 'pair' of rows to be processed
# any pairwise combination of non-empty rows could happen
# make it reproducible
set.seed(1)
idxList = matrix (sample(1:k, k), ncol = 2, byrow = TRUE)
for ( i in 1 : (nLeft / 2))
{
row1 = M[idxList[i, 1],]
row2 = M[idxList[i, 2],]
# the two columns in 'results' will become 2 rows in M
results = processRows(row1, row2)
# fill the matrix
M[nextRow, ] = results[, 1]
nextRow = nextRow + 1
M[nextRow, ] = results[, 2]
nextRow = nextRow + 1
}
cat('after fill')
print(M)