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

Hello,

To return 2 rows for each Code, one for the min and another for the max,
try the following.

I'm borrowing Bert's by() idea, it makes everything simpler.
There is a hack to have the original Code order kept, since the final
result res should have two rows for each Code, see what is order()'ed
below.


# the output has 2 consecutive rows with
# the same Code, so repeat the unique Codes
i <- order(rep(unique(df1$Code), each = 2))
res <- by(df1, df1$Code, \(x) x[c(which.min(x$Q), which.max(x$Q)), ])
res <- do.call(rbind, res)[order(i), ]

# remake the row names, they're ugly after rbind
row.names(res) <- NULL
res


Hope this helps,

Rui Barradas

?s 19:02 de 25/08/2022, javad bayat escreveu:

;Dear all
First of all I appreciate you for the answers you have sent. I did the
codes that Rui provided and I got what I wanted.
"
res <- lapply(split(df1, df1$Code), \(x) x[which.min(x$Q),])
res <- do.call(rbind, res)
i <- order(unique(df1$Code))
res[order(i), ]
"
I think I should explain more about my request. I had a large data frame
(11059 rows and 16 columns). The Code column represented the stations

code,

totally the number of stations were 128. At each station I had many
measured variables, like Q and N and O, and these variables were measured
in different years and days. The days that data were measured were
different for each station, and due to this reason I had different rows

for

stations. For example, station number one (41009) had 158 rows and

station

number 2 (41011) had 113 rows. Note that the station's codes are not in
order format (e.g smallest to largest).
Back to my request, I wanted to extract the minimum value of the Q for

each

station (based on the Code column). The problem was that I wanted to have
other column values which were measured for this minimum of the Q.
I hope my explanation was clear enough. As I said before, I used the

Rui's

codes and I got what I wanted. Although, other solutions provided by

others

were all correct.

Regarding my request, unfortunately I faced another problem. I had to
extract the maximum of the Q and put it exactly under the minimum of the

Q.

Something like the below one:
"

Code

               Y

               M

                D

            Q

             N

              O

41003

81

1

19

0.16

7.17

2.5

41003

79

8

17

10.21

5.5

7.2

41009

79

2

21

0.218

5.56

4.04
41009 79 10 20 12.24 5.3 7.1
.
.
.
.
"
I extract both min and max according to the codes, and I have 2

dataframes,

one for the minimum values and another for the max values. Both dataframe
have a Code column which is exactly similar.
Can I extract both min and max simultaneously or I have to combine two
dataframes?
I used the rbind and merge function but they did not give the desired
results.

df3 = merge (df1, df2, by = "Code")

The result of this code adds a second dataframe as columns to the first
one. I want the first row of the second dataframe put below the first row
of the first dataframe and so on. I used a function to do this but it

seems

it does not work correctly.

fun2 = function(x,y){

                 i = 1
                 for(i in x) {
                       if (x[i,1] == y[i,1]){
                           rbind(x[i,],y[i,])
                           i = i+1
                 }
                 }
                 }

fun2(df1, df2)

Sincerely




























On Thu, Aug 25, 2022 at 9:08 PM <avi.e.gross at gmail.com> wrote:

Yes, Timothy, the request was not seen by all of us as the same.

Indeed if the request was to show a subset of the original data

consisting

of only the rows that were the minimum for each Code and also showed

ties,

then the solution is a tad more complex. I would then do something along
the
lines of what others showed such as generating another column showing

the

minimum for each row and then showing only rows that matched their

value in

two columns or whatever was needed.

As noted, keeping the output in a specific order was not initially
requested.

Keeping the data in some order is a common enough request but in this
situation, I suspect the order many might want would be the one showing

the

minimums in order, not the codes in the original order.

-----Original Message-----
From: Ebert,Timothy Aaron <tebert at ufl.edu>
Sent: Thursday, August 25, 2022 11:59 AM
To: avi.e.gross at gmail.com
Cc: R-help at r-project.org
Subject: RE: [R] Getting minimum value of a column according a factor
column
of a dataframe

My assumption (maybe wrong) was that we needed to keep the other

variables.

I want to find the values of Y, M, D, N, and O for the minimum value of

Q

within each unique value of Code, keeping the data in the original

order.

All one need to do is filter Q in the original dataframe by your answer

for

minQ.

Keeping the data in the original order seems unnecessary, but that is

what

was asked in a later post.