r - Why does combining two `data.frame` objects using the `data.frame` function cut off a long variable name? -

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i have noticed if try combine 2 different data.frame objects larger data.frame using data.frame function, variable names cut off (i.e. see output of names(db) code below.

i avoid situation combining variables using data.table function instead.

my question is:

why data.frame command cut off variable names? may quite simple question, , can solved using as.data.frame function on data.table object convert data.frame, curious why variable names cut off in first place if use data.frame function. have tried looking insight using in r, , on google, have found no success far. seeking answer more me better understand how r, , data.table , data.frame works (as relatively new r user, having switched stata).

thanks in advance!

> <- data.frame(rnorm(100)) > b <- data.frame(rnorm(100)) > names(a) <- "thisisaveryverylongvariablename-mean()" > names(b) <- "thisisanotherveryverylongvariablename-std()" > db <- data.frame(a, b) > names(db) [1] "thisisaveryverylongvariablename.mean.."      "thisisanotherveryverylongvariablename.std.." > names(c(a, b)) [1] "thisisaveryverylongvariablename-mean()"      "thisisanotherveryverylongvariablename-std()" > db2 <- data.table(a, b) > names(db2) [1] "thisisaveryverylongvariablename-mean()"      "thisisanotherveryverylongvariablename-std()"

the variable names not cut-off; simply, made more "compatible" r environment. can override check.names=false argument data.frame():

a <- data.frame(rnorm(100)) b <- data.frame(rnorm(100)) names(a) <- "thisisaveryverylongvariablename-mean()" names(b) <- "thisisanotherveryverylongvariablename-std()" db <- data.frame(a, b, check.names = false) names(db) # [1] "thisisaveryverylongvariablename-mean()"      "thisisanotherveryverylongvariablename-std()"

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