R Cumulative Sum with a condition and a reset

Question

I have a signal position indicator vector consisting out of -1s and 1s. In addition, I have volume data which I want to sum based on the value of Signal. The basic data table looks like this:

df <- cbind(Signal, Volume)
head(df, 20)

           Signal    Volume
2016-01-04     NA  37912403
2016-01-05     -1  23258238
2016-01-06     -1  25096183
2016-01-07     -1  45172906
2016-01-08     -1  35402298
2016-01-11     -1  29932385
2016-01-12     -1  28395390
2016-01-13     -1  33410553
2016-01-14     -1  48658623
2016-01-15      1  46132781
2016-01-19      1  30998256
2016-01-20     -1  59051429
2016-01-21      1  30518939
2016-01-22      1  30495387
2016-01-25      1  32482015
2016-01-26     -1  26877080
2016-01-27     -1  58699359
2016-01-28      1 107475327
2016-01-29      1  62739548
2016-02-01      1  46132726

What I would like to achieve is (without using a for loop) is to produce a vector of cum Volume, which would be reset every time the Signal changes. In addition, the values of volume should be multiplied by the value of the Signal, i.e. when Signal is -1 it should add -Volume to the current cum Volume. Based on a similar questions on SO I have tried

ave(df$a, cumsum(c(F, diff(sign(diff(df$a))) != 0)*df$Volume), FUN=seq_along) 

which produces the right grouping of Signal, but the Volume is not included for some reason. Without the reset the solution is fairly straightforward (posted on SO)

require(data.table)
DT <- data.table(dt)
DT[, Cum.Sum := cumsum(Volume), by=Signal]

Does anyone know a dplyr or data.table kind of solution for both resetting and conditioning a cum sum? Thanks.

Answer 1

This can be achieved by:

library(tidyverse)
library(data.table)     

z %>%
  group_by(rleid(Signal)) %>% #advance value every time Signal changes and group by that
  mutate(cum = Signal*cumsum(Volume)) %>% #cumsum in each group
  ungroup() %>% #ungroup so you could remove the grouping column
  select(-4) #remove grouping column

or without data.table by using rle:

z %>%
  mutate(rl = rep(1:length(rle(Signal)$length), times = rle(Signal)$length)) %>%
  group_by(rl) %>%
  mutate(cum = Signal*cumsum(Volume)) %>%
  ungroup() %>%
  select(-4)

#output
    date       Signal    Volume        cum

  <fct>       <int>     <int>      <int>
 1 2016-01-04     NA  37912403         NA
 2 2016-01-05    - 1  23258238 - 23258238
 3 2016-01-06    - 1  25096183 - 48354421
 4 2016-01-07    - 1  45172906 - 93527327
 5 2016-01-08    - 1  35402298 -128929625
 6 2016-01-11    - 1  29932385 -158862010
 7 2016-01-12    - 1  28395390 -187257400
 8 2016-01-13    - 1  33410553 -220667953
 9 2016-01-14    - 1  48658623 -269326576
10 2016-01-15      1  46132781   46132781
11 2016-01-19      1  30998256   77131037
12 2016-01-20    - 1  59051429 - 59051429
13 2016-01-21      1  30518939   30518939
14 2016-01-22      1  30495387   61014326
15 2016-01-25      1  32482015   93496341
16 2016-01-26    - 1  26877080 - 26877080
17 2016-01-27    - 1  58699359 - 85576439
18 2016-01-28      1 107475327  107475327
19 2016-01-29      1  62739548  170214875
20 2016-02-01      1  46132726  216347601

data:

z <- read.table(text =      "date     Signal    Volume
           2016-01-04     NA  37912403
           2016-01-05     -1  23258238
           2016-01-06     -1  25096183
           2016-01-07     -1  45172906
           2016-01-08     -1  35402298
           2016-01-11     -1  29932385
           2016-01-12     -1  28395390
           2016-01-13     -1  33410553
           2016-01-14     -1  48658623
           2016-01-15      1  46132781
           2016-01-19      1  30998256
           2016-01-20     -1  59051429
           2016-01-21      1  30518939
           2016-01-22      1  30495387
           2016-01-25      1  32482015
           2016-01-26     -1  26877080
           2016-01-27     -1  58699359
           2016-01-28      1 107475327
           2016-01-29      1  62739548
           2016-02-01      1  46132726", header = T)

Answer 2

A pure dplyr way would be:

df %>% 
  na.omit() %>% # omit NA to not multiply by NA
  mutate(isStep = (Signal - lag(Signal, 1)) != 0) %>% # Create a dummy variable for steps 
  mutate(isStep = ifelse(is.na(isStep), FALSE, isStep)) %>% 
  mutate(grp = cumsum(isStep)) %>% # create new ID based on steps
  group_by(grp) %>%  # group by before created steps
  mutate(res = cumsum(Signal * Volume)) %>% # calculate value
  select(x, Signal, Volume, res)

# # A tibble: 19 x 5
# # Groups:   grp [6]
#      grp          x Signal    Volume        res
#    <int>     <fctr>  <int>     <int>      <int>
#  1     0 2016-01-05     -1  23258238  -23258238
#  2     0 2016-01-06     -1  25096183  -48354421
#  3     0 2016-01-07     -1  45172906  -93527327
#  4     0 2016-01-08     -1  35402298 -128929625
#  5     0 2016-01-11     -1  29932385 -158862010
#  6     0 2016-01-12     -1  28395390 -187257400
#  7     0 2016-01-13     -1  33410553 -220667953
#  8     0 2016-01-14     -1  48658623 -269326576
#  9     1 2016-01-15      1  46132781   46132781
# 10     1 2016-01-19      1  30998256   77131037
# 11     2 2016-01-20     -1  59051429  -59051429
# 12     3 2016-01-21      1  30518939   30518939
# 13     3 2016-01-22      1  30495387   61014326
# 14     3 2016-01-25      1  32482015   93496341
# 15     4 2016-01-26     -1  26877080  -26877080
# 16     4 2016-01-27     -1  58699359  -85576439
# 17     5 2016-01-28      1 107475327  107475327
# 18     5 2016-01-29      1  62739548  170214875
# 19     5 2016-02-01      1  46132726  216347601