Getting minimum value of a column according a factor column of a dataframe

I missed where you explained how to choose a minimum value if there are several values within a group that are equal to the minimum value. Here is a dplyr code that returns eight values because there are ties for minimum values in Q.

library(dplyr)
library(magrittr)
dat2<-read.table(text="Code Y M D Q N O
41003 81 1 19 0.16 7.17 2.5
41003 77 9 22 0.197 6.8 2.2
41003 79 7 28 0.21 4.7 6.2
41005 79 8 17 0.21 5.5 7.2
41005 80 10 30 0.21 6.84 2.6
41005 80 12 20 0.21 6.84 2.4
41005 79 6 14 0.217 5.61 3.55
41009 79 2 21 0.218 5.56 4.04
41009 79 5 27 0.218 6.4 3.12
41009 80 11 29 0.22 6.84 2.8
41009 78 5 28 0.232 6 3.2
41009 81 8 20 0.233 6.39 1.6
41009 79 9 30 0.24 5.6 7.5
41017 79 10 20 0.24 5.3 7.1
41017 80 7 30 0.24 6.73 2.6", header=TRUE)
dat2 <- dat2 %>%
  group_by(Code) %>%
  mutate(
    MinByCodeQ = min(Q, na.rm = T),
  ) %>%
  arrange(Code)
dat2<-filter(dat2,Q==MinByCodeQ)



Tim

-----Original Message-----
From: R-help <r-help-bounces at r-project.org> On Behalf Of javad bayat
Sent: Thursday, August 25, 2022 12:56 AM
To: Rui Barradas <ruipbarradas at sapo.pt>
Cc: R-help at r-project.org
Subject: Re: [R] Getting minimum value of a column according a factor column of a dataframe

[External Email]

Dear all,
Many thanks for your suggested methods and codes, but unfortunately they did not give the desired results.
All the codes you have provided are correct but they did not represent the whole row which is related to the minimum of "Q".
The code must result in 4 rows, with the minimum value of "Q" and other column values, as below:

       Code

              Y

              M

               D

           Q

            N

             O

41003

81

1

19

0.16

7.17

2.5

41005

79

8

17

0.21

5.5

7.2

41009

79

2

21

0.218

5.56

4.04
41017 79 10 20 0.24 5.3 7.1






Sincerely



























































































41017 79 10 20 0.24 5.3 7.1

Hello,

Here are two options, the 1st outputs a vector, the 2nd a data.frame.


x<-'41003 81 1 19 0.16 7.17 2.5
41003 77 9 22 0.197 6.8 2.2
41003 79 7 28 0.21 4.7 6.2
41005 79 8 17 0.21 5.5 7.2
41005 80 10 30 0.21 6.84 2.6
41005 80 12 20 0.21 6.84 2.4
41005 79 6 14 0.217 5.61 3.55
41009 79 2 21 0.218 5.56 4.04
41009 79 5 27 0.218 6.4 3.12
41009 80 11 29 0.22 6.84 2.8
41009 78 5 28 0.232 6 3.2
41009 81 8 20 0.233 6.39 1.6
41009 79 9 30 0.24 5.6 7.5
41017 79 10 20 0.24 5.3 7.1
41017 80 7 30 0.24 6.73 2.6'
df1 <- read.table(textConnection(x))
names(df1) <- scan(what = character(),
                    text = 'Code Y M D Q N O') df1$Code <- 
factor(df1$Code)

# 1st option
with(df1, tapply(Q, Code, min))
#  41003 41005 41009 41017
#  0.160 0.210 0.218 0.240

# 2nd option
aggregate(Q ~ Code, df1, min)
#     Code     Q
#  1 41003 0.160
#  2 41005 0.210
#  3 41009 0.218
#  4 41017 0.240


Hope this helps,

Rui Barradas

?s 08:44 de 24/08/2022, javad bayat escreveu:

Dear all;
I am trying to get the minimum value of a column based on a factor 
column of the same data frame. My data frame is like the below:
        Code               Y               M                D
  Q
      N              O
41003 81 1 19 0.16 7.17 2.5
41003 77 9 22 0.197 6.8 2.2
41003 79 7 28 0.21 4.7 6.2
41005 79 8 17 0.21 5.5 7.2
41005 80 10 30 0.21 6.84 2.6
41005 80 12 20 0.21 6.84 2.4
41005 79 6 14 0.217 5.61 3.55
41009 79 2 21 0.218 5.56 4.04
41009 79 5 27 0.218 6.4 3.12
41009 80 11 29 0.22 6.84 2.8
41009 78 5 28 0.232 6 3.2
41009 81 8 20 0.233 6.39 1.6
41009 79 9 30 0.24 5.6 7.5
41017 79 10 20 0.24 5.3 7.1
41017 80 7 30 0.24 6.73 2.6

I want to get the minimum value of the "Q" column with the whole row 
values, according to the "Code"  column  which is a factor. Overall 
it

will

give me 4 rows, with the value of "Q". Below is a code that I used 
but it did not give me what I wanted.

x[which(x$Q == min(x$Q)),]

Sincerely

--
Best Regards
Javad Bayat
M.Sc. Environment Engineering
Alternative Mail: bayat194 at yahoo.com


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