Arithmetic operation based on value from another column

问题

I have a dataframe with a value column for multiple year. The years might not follow a sequence and might have a missing 5th year. Here is an example dataframe

df = data.frame(code = c("AFG", "AGO", "ALB", "AND", "ARB", "ARE", "ARG", "ARM", "ASM", "ATG", "AUS", "AUT", "AUT", "AUT", "AUT", "ABW", "AFG", "AGO", "ALB", "AND", "ARB", "ARE", "ARG", "ARM", "ARM"),
            PPT = c(123, 42, 23, 5, 42, 4, 23, 25, 42, 23, NA, 5563, 56, 54, 645, 6, 4,53, 656, 65, 5563, 646, 6, 66, 54), 
            Year = c(1990, 1991, 1992, 1993, 1991, 1995, 1996, 1997, 1991, 1992, 2000, 2001, 2002, 2014, 2004, 2005, 2006, 2007, 1960, 2009, NA, 2011, 2012, 2013, 2014))

I want to add an additional column that will be based on the difference between the value for that year and the year+5. Ex. If the first year in the year column is 1960 but no PPT data is available for 1965, therefore the value in the new_col would be NA. Similarly, the value for new_col for the year 1990 would be 119(123-4), NA for the year 2000(no PPT data available for 2005 ), 19 for 1991 and -2 for the year 1992 and so on.

I have a very convoluted way of doing this in excel, however, I am looking for an easier solution in R

回答1:

We can arrange by 'Year', and take the difference of 'PPT' with lead of 'PPT' where the 'n' is specified as 5

library(dplyr)
df %>%
    arrange(Year) %>% 
    mutate(newcol = PPT - lead(PPT, n = 5, default = 0))
#    code  PPT Year newcol
#1   AFG  123 1990    119
#2   AGO   42 1991     19
#3   ALB   23 1992     -2
#4   AND    5 1993     -1
#5   ARB   23 1994   -611
#6   ARE    4 1995     -1
#7   ARG   23 1996  -5540
#8   ARM   25 1997    -31
#9   ASM    6 1998    -50
#10  ATG  634 1999    -11
#...

if some 'Year's are missing, we can expand the data with complete and then do the mutate

library(tidyr)
df %>% 
    arrange(Year) %>% 
    complete(Year = min(Year):max(Year)) %>%
    mutate(newcol = PPT - lead(PPT, n = 5, default = 0)) %>%
    filter(!is.na(PPT))

Or using base R

df$newcol <- with(df, c(head(PPT, -5) - tail(PPT, -5), tail(PPT, 5)))

data

df <- structure(list(code = structure(c(2L, 3L, 4L, 5L, 6L, 7L, 8L, 
9L, 10L, 11L, 12L, 13L, 13L, 13L, 13L, 1L, 2L, 3L, 4L, 5L, 6L, 
7L, 8L, 9L, 9L), .Label = c("ABW", "AFG", "AGO", "ALB", "AND", 
"ARB", "ARE", "ARG", "ARM", "ASM", "ATG", "AUS", "AUT"), class = "factor"), 
    PPT = c(123, 42, 23, 5, 23, 4, 23, 25, 6, 634, 5, 5563, 56, 
    56, 645, 6, 4, 656, 645, 65, 5563, 646, 6, 66, 54),
    Year = 1990:2014), class = "data.frame", row.names = c(NA, 
-25L))

回答2:

A data.table solution that will work with missing/gapped years...

sample data

df = data.frame(code = c("AFG", "AGO", "ALB", "AND", "ARB", "ARE", "ARG", "ARM", "ASM", "ATG", "AUS", "AUT", "AUT", "AUT", "AUT", "ABW", "AFG", "AGO", "ALB", "AND", "ARB", "ARE", "ARG", "ARM", "ARM"),
                PPT = c(123, 42, 23, 5, 23, 4, 23, 25, 6, 634, 5, 5563, 56, 56, 645, 6, 4, 656, 645, 65, 5563, 646, 6, 66, 54), 
                Year = c(1990:2014))

code

library(data.table)
#create a data.table with all years from minimum untill maximum + 5
#so missing years will get a NA!
#perform a by-reference join on these years, by Year
result <- data.table( Year = min(df$Year):(max(df$Year) + 5) )[setDT(df), `:=`(code = i.code, PPT = i.PPT), on = .(Year)]
#calculate the desired column, delete unwanted rows
result[, newcol := PPT - shift(PPT, 5, type = "lead" )][!is.na(code),][]

output

#     Year code  PPT newcol
#  1: 1990  AFG  123    119
#  2: 1991  AGO   42     19
#  3: 1992  ALB   23     -2
#  4: 1993  AND    5     -1
#  5: 1994  ARB   23   -611
#  6: 1995  ARE    4     -1
#  7: 1996  ARG   23  -5540
#  8: 1997  ARM   25    -31
#  9: 1998  ASM    6    -50
# 10: 1999  ATG  634    -11
# 11: 2000  AUS    5     -1
# 12: 2001  AUT 5563   5559
# 13: 2002  AUT   56   -600
# 14: 2003  AUT   56   -589
# 15: 2004  AUT  645    580
# 16: 2005  ABW    6  -5557
# 17: 2006  AFG    4   -642
# 18: 2007  AGO  656    650
# 19: 2008  ALB  645    579
# 20: 2009  AND   65     11
# 21: 2010  ARB 5563     NA
# 22: 2011  ARE  646     NA
# 23: 2012  ARG    6     NA
# 24: 2013  ARM   66     NA
# 25: 2014  ARM   54     NA
#     Year code  PPT newcol

回答3:

We can also use mapply

df$new_col <- mapply(function(x, y) {
     inds = df$Year == y + 5
     if (any(inds))   x - df$PPT[inds] else x
},df$PPT, df$Year)

df
#   code  PPT Year new_col
#1   AFG  123 1990     119
#2   AGO   42 1991      19
#3   ALB   23 1992      -2
#4   AND    5 1993      -1
#5   ARB   23 1994    -611
#6   ARE    4 1995      -1
#7   ARG   23 1996   -5540
#8   ARM   25 1997     -31
#9   ASM    6 1998     -50
#10  ATG  634 1999     -11
#.....

来源：https://stackoverflow.com/questions/55944339/arithmetic-operation-based-on-value-from-another-column

标签

dplyr

data.table

tidyr