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...{ if(is.na(lt[[i]])) lt[[i]] <- NULL } How to simplify for() loop by using (l)apply family? Thank you in advance. ========================================================= Dong-hyun Oh Center of Excellence for Science and Innovation Studies Royal Institute or Technology, Sweden e-mail: oh.dongh at gmail.com cel: +46 73 563 45 22

Dear UseRs, I would like to know the way to find classes of each column of data.frame(). Thank you in advance. ========================================================= Dong-hyun Oh Center of Excellence for Science and Innovation Studies Royal Institute or Technology, Sweden e-mail: oh.dongh at gmail.com cel: +46 73 563 45 22

...want is as follows: > dt a b c test1 test2 1 3 2 1 2 2 2 3 1 2 3 2 5 1 2 Any help? Thank you in advance. Best, ========================================================= Dong-hyun Oh Center of Excellence for Science and Innovation Studies Royal Institute or Technology, Sweden e-mail: oh.dongh at gmail.com cel: +46 73 563 45 22

...similar to str_replace() in php exists in R. Looking forward to hearing from you. Best, ========================================================= Center of Excellence for Science and Innovation Studies, Royal Institute of Technology Drottning Kristinas v?g 30 100 44 Stockholm, Sweden e-mail: donghoh at infra.kth.se, doriaba2 at snu.ac.kr, oh.dongh at gmail.com Office: +46 8 790 67 93 Fax: +46 8 790 95 17 Cell phone: +46 73 563 45 22 =========================================================

...it faster in help.search()? I think indexing help database is one of the solution, but i don't know how to do. Best, Dong-hyun Oh ========================================================= Center of Excellence for Science and Innovation Studies, Royal Institute of Technology, Sweden e-mail: donghoh at infra.kth.se, doriaba2 at snu.ac.kr, oh.dongh at gmail.com cell phone: +46 73 563 45 22

...le to restrict coefficients, it is possible to restrict coefficients of factors? If so, how? Thanks in advance. Best, ========================================================= Dong-hyun Oh Center of Excellence for Science and Innovation Studies Royal Institute or Technology, Sweden e-mail: oh.dongh at gmail.com cel: +46 73 563 45 22

Hi, my data set is data.frame(id, yr, y, l, e, k). I would like to estimate Lee and Schmidts (1993, OUP) model in R. My colleague wrote SAS code as follows: ** procedures for creating dummy variables are omitted ** ** di# and dt# are dummy variables for industry and time ** data a2; merge a1 a2 a; by id yr; proc sysnlin maxit=100 outest=beta2; endogenous y; exogenous l e k