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

Sat Oct 14 12:26:57 CEST 2017

Dear @Eric<mailto:ericjberger at gmail.com>, thank you so very much for noticing that. When I tested @Rui<mailto:ruipbarradas at sapo.pt>’s solution, it was on a smaller dataset that had purely matching rows. I had considered including non-matching rows to evaluate what the alternative would be.

Also, I hadn’t even tested it on the larger dataset. I have now and noticed that it went further to omit rows that did not match, just like you said.

Your proposed solution works well.

Much appreciated…I’ll get in touch in case I encounter any problems

From: Eric Berger <ericjberger at gmail.com>
Date: Saturday, 14 October 2017 at 12:43
To: Kevin Wamae <KWamae at kemri-wellcome.org>
Cc: Rui Barradas <ruipbarradas at sapo.pt>, "r-help at r-project.org" <r-help at r-project.org>
Subject: Re: [R] Populate one data frame with values from another dataframe for rows that match

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<http://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<mailto: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<mailto: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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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

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