Rename aggregated columns using data.table in R

Question

I have a table dtTrain which has many columns. I am trying to perform 4 aggregation columns on each, [Min, Max, sd, mean]. To do this I am running the line

subTrain <- dtTrain[,c(min = lapply(.SD, min), 
                       max = lapply(.SD, max), 
                       sd = lapply(.SD, sd), 
                       mean = lapply(.SD, mean)), by=TrialID]

The problem I am having is the aggregation is working but the column headers are repeated (ie column1 is produced four times in the subTrain table). I would prefer [column1.min,...,column1.max...,column1.sd, ...column1.mean,...] or in fact any column label.

See also: Calculate multiple aggregations with lapply(.SD, …); Apply multiple functions to multiple columns in data.table — Henrik
– Henrik, Commented Nov 28, 2018 at 10:30

akrun · Accepted Answer · 2016-06-06 08:48:44Z

1

We can use setnames with rep to change the column names

res <- dtTrain[, c(lapply(.SD, min), 
        lapply(.SD, max),
        lapply(.SD, sd), 
       lapply(.SD, mean)), by=TrialID]
nm1 <- setdiff(names(dtTrain), 'TrialID')
setnames(res, 2:ncol(res), paste(nm1, rep(c('min', 'max', 'sd', 'mean'), 
                         each = length(nm1)), sep="."))

edited Jun 6, 2016 at 8:48

answered Jun 6, 2016 at 7:41

akrun

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3 Comments

wbm Over a year ago

res1 <- setnames(res, 1:(length(res)-1), paste(nm1, rep(c('min', 'max', 'sd', 'mean'), each = length(nm1)), sep=".")) works

Uwe Over a year ago

Please, can either akrun or @wbm correct the final answer? Thank you.

wbm Over a year ago

yes, correct. I thought everything in R was zero base but a bit of a newbie. Many thanks @akrun

Sowmya S. Manian · Accepted Answer · 2016-06-06 07:59:29Z

0

Changing of column names can be done using names() function or colnames() function

 > names(Result_dataframe) <- c("Min","Max","sd","Mean")

 #                         OR

 > colnames(Result_dataframe) <- c("Min","Max","sd","Mean")

answered Jun 6, 2016 at 7:59

Sowmya S. Manian

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