Data frame to matrix in R - r

Question

In R, I am using a for loop to iterate through a large data frame, trying to put the integer in the *i*th row, 7th column into a specific index in another matrix. The specific index corresponds to the index in the large data frame (again in the *i*th row, but the 2nd and 4th column instead). For example, say that my data frame has data_frame[1,2]=5, data_frame[1,4]=12, and data_frame[1,7]=375. I want to put 375 into my matrix in the index where the row has the name 5 and the column has name 12.
However, the problem (I think) is that when I do col_index=which(colnames(matrix)==data_frame[1,2]), it returns integer 0. The column name is technically 5, but I noticed it only works if I do col_index=which(colnames(matrix)=="5"). How can I make sure that (in my for loop) data_frame[i,2] corresponds to "5"?
data is saved as "out" My matrix that I want to put the data in is called "m"
m=matrix(nrow=87,ncol=87)
fips=sprintf("%03d",seq(1,173,by=2))
colnames(m)=fips
rownames(m)=fips
m[1:40,1:40]
Next, the condition that the 3rd column is equal to 27
for(i in 8:2446)
{
if(out[i,3]==27)
{
out_col=out[i,4]
out_row=out[i,2]
moves=out[i,7]
col_index=which(colnames(m)==paste(out_col))
row_index=which(rownames(m)==paste(out_row))
m[row_index,col_index]=moves
}
}
Sorry for the lack of formatting. It is putting numbers in the matrix, but they aren't the right numbers, and I can't figure out what's wrong. Any help would be much appreciated!

Answer 1

There's a lot of complexity in your example, but it boils down to replacing values in mat, where the row name, column name, and new value are stored in out. Let's start with a reproducible example (it would have been helpful if you posted one!)
# Matrix to have values replaced
mat <- matrix(0, nrow=3, ncol=3)
rownames(mat) <- c("1", "2", "3")
colnames(mat) <- c("4", "5", "6")
mat
# 4 5 6
# 1 0 0 0
# 2 0 0 0
# 3 0 0 0
out <- data.frame(row=c(1, 3, 3), col=c(6, 5, 4), val=c(1, 4, -1))
out
# row col val
# 1 1 6 1
# 2 3 5 4
# 3 3 4 -1
Now, doing the replacement is a one-liner:
mat[cbind(as.character(out$row), as.character(out$col))] <- out$val
mat
# 4 5 6
# 1 0 0 1
# 2 0 0 0
# 3 -1 4 0
Basically, we're indexing mat by a 2-column matrix, where each row of the indexing matrix is a row name and column name.
In your example, you appear to be excluding the first 7 rows of out, as well as any row where out[,3] does not equal 27. You could simply subset out based on these requirements with something like realout <- out[out[,3] == 27 & seq(nrow(out)) %in% 8:2446,] and then do the replacement with realout.
Note that one added benefit of doing the replacement in this way is that it will be much faster than using a for loop through the rows of out.