This question already has answers here:
Convert a matrix to a 1 dimensional array
(11 answers)
Closed 4 years ago.
I have a matrix measuring 91 x 2 (i.e 91 rows and two columns).
mat1 <- matrix(1:182, 91, 2)
I need to create a vector from the said matrix of one row. I can do that with the following:
mat2 <- matrix(mat1, nrow = 1, byrow = TRUE).
However, I would like to have each row in the original matrix to be represented one after another. Currently it's taking all of column 1 then all of column 2 and joining those together sequentially. Whilst I need them to be in one long row, like this: 1,92,2,93,3,94 etcMeaning the structure ultimately would be 1,182 (i.e. one row with 182 columns).
How can I achieve this?
Thanks.
We can transpose the matrix and convert it to a vector
c(t(mat1))
Related
This question already has answers here:
Sum elements of a vector beween zeros in R
(3 answers)
Closed 2 years ago.
I want to add values from a column. They go in sequence:
0,225,2352,34234,23442,23456,0,123,...
I want to add the values from 0 until the following 0 but not including the second.
For example, i want an output of
(0+225+2352+34234+23442+23456),(0+123+,...,),...
I want to store them as a new column of totals
One simple solution in base R is
sapply(split(x, cumsum(x == 0)), sum)
With split you basically create groups of elements that you want to sum together using sapply. The final result will be a named numeric vector.
Sample data
x <- c(0,225,2352,34234,23442,23456,0,123,2,0,1,42)
sapply(split(x, cumsum(x == 0)), sum)
# 1 2 3
# 83709 125 43
This question already has answers here:
How to index a vector sequence within a vector sequence
(5 answers)
Closed 5 years ago.
I have got a dataframe and I need to find row numbers where the values of the entries in one column match a certain pattern.
Let the col1 col1 = matrix(c(1,0,0,0,0,0,0,0,0,0,2,0,2,0,0,0,0,0,0,0,1), nrow = 21, ncol = 1) be an example of by column and vector r r = c(2, 0 ,2) be a vector I need to match it with.
I need R to return an index number of rows where the pattern in r matches the values in col1 (in this case row 11, 12, 13).
I thought I could achieve this with row.match, but that is not the case. I have tried different combinations of match function, but it doesn't yield any results either.
Maybe the way I am approaching this problem is wrong from the beginning, but I have trouble believing that there isn't any function, that would provide me with the expected result given some adjustment.
Thanks.
You could do this using rollapply from zoo. Basically, this runs identical on a rolling basis with a window of length(r). This tells you that the sequence is present starting at positon 11 of the col1 vector..
library(zoo)
which(rollapply(col1,length(r),identical,r))
[1] 11
To get a vector of positions, you could do:
which(rollapply(col1,length(r),identical,r))+0:(length(r)-1)
[1] 11 12 13
This question already has answers here:
Element-wise mean over list of matrices [duplicate]
(2 answers)
Closed 6 years ago.
For example, I have a list of matrix like this
list2<-lapply(1:2, function(x) matrix(rnorm(6, 10, 1), nrow=2, ncol=3))
list2
How do I get a matrix which has the same size with each matrix in each list, and the value in each cell equal to the average of corresponding cell across lists.
We can do this by adding the corresponding cells in each list elements and divide by the length of the list
Reduce(`+`, list2)/length(list2)
Or another option is to unlist the list, create a 3D array, use apply to get the mean
apply(array(unlist(list2), c(2,3,2)), c(1,2), mean)
This question already has answers here:
Sum rows in data.frame or matrix
(7 answers)
Closed 7 years ago.
I need to sum columns of a table that have a names starting with a particular string.
An example table might be:
tbl<-data.frame(num1=c(3,2,9), num2=c(3,2,9),n3=c(3,2,9),char1=c('a', 'b', 'c'))
I get the list of columns (in this example I wrote only 2, but the real case has more tan 20).
a<-colnames(tbl)[grep('num', colnames(tbl))]
I tried with
sum(tbl[,a])
But I get only one number with the total sum of the elements in both vectors.
What I need is the result of:
tbl$num1+ tbl$num2
We can either use Reduce
Reduce(`+`, tbl[a])
Or rowSums. The rowSums also has the option of removing the NA elements with na.rm=TRUE.
rowSums(tbl[a])
This question already has answers here:
Extract matrix column values by matrix column name
(2 answers)
Closed 7 years ago.
In R I can access the data in a column vector of a column matrix by the following:
mat2[,1]
Each column of mat2 has a name. How can I retrieve the data from the first column by using the name attribute instead of [,1]?
For example suppose my first column had the name "saturn". I want something like
mat2[,1] == mat2[saturn]
The following should do it:
mat2[,'saturn']
For example:
> x <- matrix(1:21, nrow=7, ncol=3)
> colnames(x) <- paste('name', 1:3)
> x[,'name 1']
[1] 1 2 3 4 5 6 7
Bonus information (adding to the first answer)
x[,c('name 1','name 2')]
would return two columns just as if you had done
x[,1:2]
And finally, the same operations can be used to subset rows
x[1:2,]
And if rows were named...
x[c('row 1','row 2'),]
Note the position of the comma within the brackets and with respect to the indices.