Select rows of a matrix that meet a condition
m <- matrix(1:20, ncol = 4)
colnames(m) <- letters[1:4]
The following command will select the first row of the matrix above.
subset(m, m[,4] == 16)
And this will select the last three.
subset(m, m[,4] > 17)
The result will be a matrix in both cases. If you want to use column names to select columns then you would be best off converting it to a dataframe with
mf <- data.frame(m)
Then you can select with
mf[ mf$a == 16, ]
Or, you could use the subset command.
This is easier to do if you convert your matrix to a data frame using as.data.frame(). In that case the previous answers (using subset or m$three) will work, otherwise they will not.
To perform the operation on a matrix, you can define a column by name:
m[m[, "three"] == 11,]
Or by number:
m[m[,3] == 11,]
Note that if only one row matches, the result is an integer vector, not a matrix.
I will choose a simple approach using the dplyr package.
If the dataframe is data.
library(dplyr)
result <- filter(data, three == 11)