CODEWITHSUNDEEP
rloops
antonina
antonina

Reputation: 109

Calculate balance value between year and year before in R

I am trying to get a balance value from a df that looks like this

df1

Name   Year    Ch1    Origin
A      1995    x1      a
A      1996    x2      b
A      1997    x3      a
A      2000    x4      a
B      1997    y1      c
B      1998    y2      c

while Ch1 is numerical. and I want to add an extra col to have this value:

Name   Year   Ch1    Bil
A      1995    x1    
A      1996    x2    %
A      1997    x3    %
A      2000    x4    %
B      1997    y1  
B      1998    y2    %

I want "Bil" to be Xi/Xi-1 (value from previous year divided by recent year) IF Xi>=Xi-1 and -Xi-1/Xi IF Xi<Xi-1 while i is a Year and i-1 is the year before.

I know I can loop this like:

for (i in nrow(df1))
  if (df[i,1]==df[i-1,1]) {
      if (df[i,3]>df[i-1,3] {
          df$Bil<-(df[i,3]/df[i-1,3])
      } else df$Bil<-(-df[i-1,3]/df[i,3])
  }

Is there a more elegant or quicker way to calculate this? This way I really need to make sure that the dataset is in the right order (going from older to recent years).

Upvotes: 1

Views: 159

Answers (2)

Ian Campbell
Ian Campbell

Reputation: 24790

We can use lag from dplyr.

library(dplyr)
df1 %>% 
  arrange(Year) %>% 
  group_by(Name) %>% 
  mutate(Bil = case_when(Ch1 >= lag(Ch1) ~ Ch1 / lag(Ch1), 
                         Ch1 < lag(Ch1) ~ -lag(Ch1)/Ch1))

Data

df1 <- structure(list(Name = structure(c(1L, 1L, 1L, 1L, 2L, 2L), .Label = c("A", 
"B"), class = "factor"), Year = c(1995L, 1996L, 1997L, 2000L, 
1997L, 1998L), Ch1 = structure(1:6, .Label = c("x1", "x2", "x3", 
"x4", "y1", "y2"), class = "factor"), Origin = structure(c(1L, 
2L, 1L, 1L, 3L, 3L), .Label = c("a", "b", "c"), class = "factor")), class = "data.frame", row.names = c(NA, 
-6L))
df1<-df1 %>% mutate(Ch1 = round(runif(n=6,100,1000),2))

Upvotes: 1

Gautam
Gautam

Reputation: 2753

Here's a data.table approach using shift.

library(data.table)
dat <- as.data.table(df1)

dat$value <- rnorm(6, 20, 1) #adding a numeric column 

dat1 <- dat[order(Year)][, 
             Bil := ifelse(test = shift(x = value, n = 1, type = 'lag') > value, 
                           yes = shift(x = value, n = 1, type = 'lag')/value, 
                           no = value/shift(x = value, n = 1, type = 'lag'))]

> dat
   Name Year Ch1 Origin    value
1:    A 1995  x1      a 19.23394
2:    A 1996  x2      b 21.16079
3:    A 1997  x3      a 20.87078
4:    A 2000  x4      a 20.50770
5:    B 1997  y1      c 20.39450
6:    B 1998  y2      c 20.53281

> dat1
   Name Year Ch1 Origin    value      Bil
1:    A 1995  x1      a 19.23394       NA
2:    A 1996  x2      b 21.16079 1.100179
3:    A 1997  x3      a 20.87078 1.013895
4:    B 1997  y1      c 20.39450 1.023353
5:    B 1998  y2      c 20.53281 1.006782
6:    A 2000  x4      a 20.50770 1.001224

Upvotes: 0

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