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mindlessgreen
mindlessgreen

Reputation: 12102

R Sort/Order dataframes using variables

My question is similar to few other sorting/ordering questions but not the same. The question is basically how to sort/order dataframes or datatables in R when the column to sort by is stored in a variable.

Say I have a data frame

#create data frame
df <- data.frame(a=c(2,2,2,2,1,1,3,3,3,3,4,4),
                 b=c("c","c","a","a","a","b","b","d","d","d","e","e"),
                 c=c(123,223,1232,122,1232,345,243,456,5676,34,233,111),
                 stringsAsFactors=F)

There are numerous ways to order the dataframe. Some of the base approaches are:

#ordering dataframe by column 1
df[with(df,order(df[,1])), ]
#ordering dataframe by column name 'a'
df[with(df,order(df[,"a"])), ]

Similarly, with datatables:

library(data.table)
dt <- as.data.table(df)
dt[order(a)]

But, if my column to order by is stored in a variable var, how do I use that?

#sort by column 1
var <- 1

#sort by column name "a"
var <- "a"

Taking a step further, how do I sort by multiple columns?

#sort by columns 1 and 2
var1 <- 1
var2 <- 2

Upvotes: 1

Views: 1921

Answers (1)

road_to_quantdom
road_to_quantdom

Reputation: 1361

try this

df[order(df[[var]]),]

EDIT thanks to David or this if you have multiple conditions

df[order(df[,var]),]

Upvotes: 1

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