Dear R forum,

I have following data.frame -

my_dat = data.frame(sr = c(0,0,0,0, 1, 1, 1, 1, 2, 2, 2, 2), bond = c("A", "B", "B", "B", "A", "B", "B", "B", "A", "B", "B", "B"), cashflow = c(1000, 2000, 2000, 4000, 10, 200, 300, 100, 80, 40, 60, 120))

> my_dat
   sr   bond  cashflow
1   0    A     1000
2   0    B     2000
3   0    B     2000
4   0    B     4000
5   1    A       10
6   1    B      200
7   1    B      300
8   1    B      100
9   2    A       80
10  2    B       40
11  2    B       60
12  2    B      120

The above data.frame is just an example. My original data is bit large. My requirement is for given sr no, I need to add the cashflow values, for each bond. Thus, I need the output (as a data.frame) as -


# OUTPUT

  sr bond cashflow_total
1  0    A           1000
2  0    B           8000
3  1    A             10
4  1    B            600
5  2    A             80
6  2    B            220

My - code

my_dat$key = paste(my_dat$bond, my_dat$sr, sep = "_")
cashflow_total = tapply(my_dat$cashflow, my_dat$key, sum)

> cashflow_total
 A_0  A_1  A_2  B_0  B_1  B_2 
1000   10   80 8000  600  220

How do maintain the original order of sr and bond as in my_dat data.frame and obtain the 

above OUTPUT?

Kindly guide. 

Anna
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