CODEWITHSUNDEEP
rdata.table
Eric
Eric

Reputation: 67

finding corresponding value for minimal number - r

I have a data frame, where I would like to get the corresponding values the min value. 

library(data.table)
df <- data.frame(cbind(c(1,1,1,1,2,2,2,2), 
                       c(180,170,180,190,160,170,170,180),
                       c(80,75,76,81,67,65,66,70), 
                       c(5,6,7,8,9,5,6,7)
                 ))

df_stat <- setDT(df)[, list(
             min = min(X2)
            ), by = X1]

The outcome should be looking like

df_stat <- data.frame(cbind(c(1,2),
                            c(170,160),
                            c(75,67),
                            c(6,9)
                    ))

I have tried with which.min and others but they did not provide the right result. Thanks in advance. Eric

Upvotes: 2

Views: 99

Answers (1)

David Arenburg
David Arenburg

Reputation: 92282

You can use .SD on your original data

setDT(df)
df[, .SD[which.min(X2)], by = X1]
#    X1  X2 X3 X4
# 1:  1 170 75  6
# 2:  2 160 67  9

Or you could sort by X1 and X2 and select unique X1

unique(setorder(df, X1, X2), by = "X1")
#    X1  X2 X3 X4
# 1:  1 170 75  6
# 2:  2 160 67  9

Or create an index using .I and then subset by it

indx <- df[, .I[which.min(X2)], by = X1]$V1
df[indx]
#    X1  X2 X3 X4
# 1:  1 170 75  6
# 2:  2 160 67  9

Upvotes: 4

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