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# c++ armadillo cast/convert to integer type vector or matrix

Date : November 17 2020, 04:28 AM
To fix the issue you can do If you are just dealing with positive values, then the conv_to function of the armadillo package will do exactly the same as the method you are trying to use.
code :
``````vec t = linspace(0, 100);
double freq = 0.25;
ivec indices = conv_to<ivec>::from(t / freq);
``````
``````ivec indices = conv_to<ivec>::from(floor(t / freq));
``````

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By : ricxsar
Date : March 29 2020, 07:55 AM
wish of those help It shouldn't be so hard to achieve similar behavior with reshape I think:
code :
``````mat vec2mat(vec V, size_t cols) {
size_t rows = std::ceil(V.n_elems / double(cols));
return V.reshape(cols, rows);// return the original vector as matrix
}
``````

## How do I convert an armadillo matrix to a vector of vectors?

By : user3336040
Date : March 29 2020, 07:55 AM
Hope this helps In such cases you should use arma::conv_to which is a totally superb feature of arma.
Note that this method will require from a source object to be able to be interpreted as a vector. That is why we need to do this iteratively for every row. Here is a conversion method:
code :
``````#include <armadillo>

typedef std::vector<double> stdvec;
typedef std::vector< std::vector<double> > stdvecvec;

stdvecvec mat_to_std_vec(arma::mat &A) {
stdvecvec V(A.n_rows);
for (size_t i = 0; i < A.n_rows; ++i) {
V[i] = arma::conv_to< stdvec >::from(A.row(i));
};
return V;
}
``````
``````#include <iomanip>
#include <iostream>

int main(int argc, char **argv) {
arma::mat A = arma::randu<arma::mat>(5, 5);
std::cout << A << std::endl;

stdvecvec V = mat_to_std_vec(A);
for (size_t i = 0; i < V.size(); ++i) {
for (size_t j = 0; j < V[i].size(); ++j) {
std::cout << "   "
<< std::fixed << std::setprecision(4) << V[i][j];
}
std::cout << std::endl;
}
return 0;
}
``````
``````0.8402   0.1976   0.4774   0.9162   0.0163
0.3944   0.3352   0.6289   0.6357   0.2429
0.7831   0.7682   0.3648   0.7173   0.1372
0.7984   0.2778   0.5134   0.1416   0.8042
0.9116   0.5540   0.9522   0.6070   0.1567

0.8402   0.1976   0.4774   0.9162   0.0163
0.3944   0.3352   0.6289   0.6357   0.2429
0.7831   0.7682   0.3648   0.7173   0.1372
0.7984   0.2778   0.5134   0.1416   0.8042
0.9116   0.5540   0.9522   0.6070   0.1567
``````

## Efficient copying/casting of large matrix std::vector<std::vector<double>> and armadillo arma::mat

By : Christina Renteria
Date : March 29 2020, 07:55 AM
around this issue You can probably avoid the copy by changing a bit the way you use your vectors/memory.
If you look at the documentation

## Idiomatic matrix type conversion, say convert Integer (0/1) matrix to boolean matrix

By : Dmitry Shelya
Date : March 29 2020, 07:55 AM
Hope that helps mode(B) <- "logical" or "mode<-"(B, "logical"). We can also use storage.mode function.
This workaround is good for two reasons:
code :
``````## an integer matrix
A <- matrix(1:4, nrow = 2, dimnames = list(letters[1:2], LETTERS[1:2]))
#  A B
#a 1 3
#b 2 4
``````
``````"mode<-"(A, "numeric")
#  A B
#a 1 3
#b 2 4

"mode<-"(A, "logical")
#     A    B
#a TRUE TRUE
#b TRUE TRUE

"mode<-"(A, "chracter")
#  A   B
#a "1" "3"
#b "2" "4"

"mode<-"(A, "complex")
#     A    B
#a 1+0i 3+0i
#b 2+0i 4+0i

str("mode<-"(A, "list"))  ## matrix list
#List of 4
# \$ : int 1
# \$ : int 2
# \$ : int 3
# \$ : int 4
# - attr(*, "dim")= int [1:2] 2 2
# - attr(*, "dimnames")=List of 2
#  ..\$ : chr [1:2] "a" "b"
#  ..\$ : chr [1:2] "A" "B"
``````
``````f <- factor(c("a", "b"))

## this "surprisingly" doesn't work
mode(f) <- "character"
#Error in `mode<-`(`*tmp*`, value = "character") :
#  invalid to change the storage mode of a factor

## this also doesn't work
mode(f) <- "numeric"
#Error in `mode<-`(`*tmp*`, value = "numeric") :
#  invalid to change the storage mode of a factor

## this does not give any error but also does not change anything
## because a factor variable is internally coded as integer with "factor" class
mode(f) <- "integer"
f
#[1] a b
#Levels: a b
``````

## How do i convert a vector into armadillo matrix?

By : Allen Gaminde
Date : March 29 2020, 07:55 AM
help you fix your problem I have a vector that contains a list of integers. How do i convert that vector into an armadillo matrix with only 1 column and the number or rows as the length of the vector? , I think you can use:
code :
``````mat A = conv_to<mat>::from(your_vector)
``````