[R] Populate one data frame with values from another dataframe for rows that match

[Eric Berger]

Hi Kevin,
I think there are issues with Rui's proposed solution. For example, if
there are rows in myDF1 which have a studyno
which does not match any row in myDF2, then you will lose those rows. In
your original request you said that you wanted to keep those rows.

To demonstrate my point I need to modify your sample data. Specifically, I
changed some studyno settings in myDF1, and also the entries of pf_mcl in
myDF1.

myDF1 <- structure(list(studyno = c("J1000/8", "J1000/9", "J1000/9",
"J1000/9",
"J1000/5", "J1000/6"), date = structure(c(17123, 17127, 17135,
17144, 17148, 17155), class = "Date"), pf_mcl = c(1:6
), year = c(2016, 2016, 2016, 2016, 2016, 2016)), .Names = c("studyno",
"date", "pf_mcl", "year"), row.names = c(NA, 6L), class = "data.frame")

myDF2 <- structure(list(studyno = c("J740/4", "J1000/9", "J895/7", "J931/6",
"J609/1", "J941/3"), pf_mcl = c(0L, 0L, 0L, 0L, 0L, 0L)), .Names =
c("studyno",
"pf_mcl"), row.names = c(NA, 6L), class = "data.frame")

#Rui's proposal gives the following result
# studyno       date year pf_mcl
# 1 J1000/9 2016-11-22 2016      0
# 2 J1000/9 2016-11-30 2016      0
# 3 J1000/9 2016-12-09 2016      0

My proposal

library(dplyr)

myDF1$studyno <- as.character(myDF1$studyno)
myDF2$studyno <- as.character(myDF2$studyno)
myDF3 <- merge(myDF1, myDF2, by="studyno", all.x=TRUE ) %>%
                dplyr::mutate( pf_mcl = ifelse( is.na(pf_mcl.y), pf_mcl.x,
pf_mcl.y ) ) %>%
                dplyr::select( studyno, date, pf_mcl )

# The results of this approach
#  studyno       date pf_mcl
# 1 J1000/5 2016-12-13      5
# 2 J1000/6 2016-12-20      6
# 3 J1000/8 2016-11-18      1
# 4 J1000/9 2016-11-22      0
# 5 J1000/9 2016-11-30      0
# 6 J1000/9 2016-12-09      0

Comparing the two results you see that no rows have been dropped in my
approach.

HTH,

Eric





On Sat, Oct 14, 2017 at 8:49 AM, Kevin Wamae <KWamae at kemri-wellcome.org>
wrote:

> Dear @Rui Barradas, thank you for the solution. It works perfectly.
>
>
> On 13/10/2017, 23:35, "Rui Barradas" <ruipbarradas at sapo.pt> wrote:
>
>     Hello,
>
>     Try the following.
>
>
>     myDF1$studyno <- as.character(myDF1$studyno)
>     myDF2$studyno <- as.character(myDF2$studyno)
>     i1 <- which(names(myDF1) == "pf_mcl")
>
>     merge(myDF1[-i1], myDF2, by = "studyno")
>
>
>     Hope this helps,
>
>     Rui Barradas
>
>     Em 13-10-2017 20:09, Kevin Wamae escreveu:
>     > I'm trying to populate the column “pf_mcl” in myDF1 with values from
> myDF2, where rows match based on column "studyno" but the solutions I have
> found so far don't seem to be giving me the desired output.
>     >
>     > Below is a snapshot of the data.frames.
>     >
>     > myDF1 <- structure(list(studyno = c("J1000/9", "J1000/9", "J1000/9",
> "J1000/9",
>     > "J1000/9", "J1000/9"), date = structure(c(17123, 17127, 17135,
>     > 17144, 17148, 17155), class = "Date"), pf_mcl = c(NA_integer_,
>     > NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_
>     > ), year = c(2016, 2016, 2016, 2016, 2016, 2016)), .Names =
> c("studyno",
>     > "date", "pf_mcl", "year"), row.names = c(NA, 6L), class =
> "data.frame")
>     >
>     > myDF2 <- structure(list(studyno = c("J740/4", "J1000/9", "J895/7",
> "J931/6",
>     > "J609/1", "J941/3"), pf_mcl = c(0L, 0L, 0L, 0L, 0L, 0L)), .Names =
> c("studyno",
>     > "pf_mcl"), row.names = c(NA, 6L), class = "data.frame")
>     >
>     > myDF2 is a well curated subset of myDF1. Some rows in the two
> datasets match based on "studyno", one may find that values are missing in
> myDF1$pf_mcl or the values are wrong.
>     >
>     > All I want to do is identify a matching row in myDF2 and populate
> myDF1$pf_mcl with the value in myDF2$pf_mcl. If a row does not match based
> on “studyno”, the value should remain the same.
>     >
>     > It's probably worth mentioning, the two data frames have other
> columns...I have selected a few for example purposes.
>     >
>     >
>     >
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