Somatoria accumulating columns in a matrix in R

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7

I have the following situation:

In a numeric matrix type: 

Temp <- matrix(runif(25, 10, 100),nrow=5,ncol=5)

V1    V2    V3    V4    V5

11    34    45    54    55
16    21    45    75    61
88    49    85    21    22
12    13    12    11    10
69    45    75    78    89

How to transform this matrix into a matrix that is the cumulative sum of columns? The result would be as follows 

V1    V2    V3    V4    V5

11    45    90    144   199
16    37    82    157   218
88    137   222   243   265
12    25    37    48    58
69    114   189   267   356

I have achieved the goal using a for loop, but I believe there should be a more efficient way to do it since I am working with a 2580-matrix matrix for 253 columns and it takes a while to generate the result 

Temp <- matrix(runif(25, 10, 100),nrow=5,ncol=5)
Temp <- round(Temp,0)
sum_matrix <- matrix(0,nrow=nrow(Temp),ncol=ncol(Temp))
sum_matrix[,1] <- Temp[,1]
    for (n in 2:nrow(Temp)) {
        sum_matrix[,n] <- sum_matrix[,n-1] + Temp[,n]
}
    
asked by anonymous 25.04.2016 / 23:10

2 answers

6

You can use the cumsum function to get the cum ulative sum . And apply , added to t (transpose) can be used to get the result you need: 

temp <- t(matrix(c(11, 34, 45, 54, 55,
                   16, 21, 45, 75, 61,
                   88, 49, 85, 21, 22,
                   12, 13, 12, 11, 10,
                   69, 45, 75, 78, 89)
    ,nrow=5,ncol=5))
temp2 <- t(apply(temp, 1, cumsum))
temp2

     [,1] [,2] [,3] [,4] [,5]
[1,]   11   45   90  144  199
[2,]   16   37   82  157  218
[3,]   88  137  222  243  265
[4,]   12   25   37   48   58
[5,]   69  114  189  267  356
    
26.04.2016 / 00:30
1

A form using the dplyr and tidyr packages would be as follows: 

> library(tidyr)
> library(dplyr)
> 
> temp <- matrix(1:25, 5, 5)
> temp <- data.frame(id = 1:5, temp)
> temp
  id X1 X2 X3 X4 X5
1  1  1  6 11 16 21
2  2  2  7 12 17 22
3  3  3  8 13 18 23
4  4  4  9 14 19 24
5  5  5 10 15 20 25
> temp %>%
+   gather(variavel, valor, -id) %>%
+   group_by(id) %>%
+   arrange(variavel) %>%
+   mutate(valor = cumsum(valor)) %>%
+   spread(variavel, valor)
Source: local data frame [5 x 6]

     id    X1    X2    X3    X4    X5
  (int) (int) (int) (int) (int) (int)
1     1     1     7    18    34    55
2     2     2     9    21    38    60
3     3     3    11    24    42    65
4     4     4    13    27    46    70
5     5     5    15    30    50    75

To use this format, your data must be stored in a data.frame.

Note that if this type of manipulation makes sense in your database, it means that it is not in tidy format. To further understand why the tidy format is ideal for use in R, it is well worth read this article from Hadley .

    
26.04.2016 / 03:12
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