Find duplicate values in a column A and compare dates in column B

Asked Nov 23 '16 at 10:41

Active Nov 23 '16 at 10:41

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I got a data frame like this:

Source: | Date:
A         2015-12-03
A         2015-11-01
B         2015-12-01
A         2015-10-04
C         2015-11-01
C         2015-11-12

I wish to create a new data frame were there is only one instance per unique Source value with the earliest Date value. Like so:

Source: | Date:
A         2015-10-04
B         2015-12-01
C         2015-11-01

It is simple enough to get unique source values, but I find it hard to come up with a solution to check if Source is a duplicate and if so save the earliest Date.

Anyone got a simple way for solving this?

asked Nov 23 '16 at 10:41

Arefo

1

Without using packages I would do `df <- df[order(as.Date(df$Date)), ] ; df[!duplicated(df$Source),]`. Using packages I would go with `library(data.table) ; unique(setDT(df)[order(as.Date(Date))], by = "Source")` – David Arenburg Nov 23 '16 at 10:46
dplyr: `df %>% group_by(Source) %>% summarise(Date = min(Date))` – Jacob Nov 23 '16 at 10:58
Worked as a charm! – Arefo Nov 23 '16 at 11:01

Find duplicate values in a column A and compare dates in column B

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