<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">Data.table is a column-based data structure. Row wise operations are going to be not as clean or efficient. rowSums() converts the input to a matrix first which is inefficient. But we plan to take care of that in the future releases.</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">I’d do something like:</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">cols = split(grep(“^pop”, names(dt), value=TRUE), rep(1:3, each=3))</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">ans = lapply(cols, function(col) dt[, rowSums(.SD, na.rm=TRUE), by=.(origin, race, sex, year, total_pop), .SDcols = col])</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">You can then bind these together however you wish. I don’t think there’s a cleaner way to do this, unless you reshape your data into long form. See the reshaping vignette in the Getting started wiki - <a href="https://github.com/Rdatatable/data.table/wiki/Getting-started">https://github.com/Rdatatable/data.table/wiki/Getting-started</a> in case you’re interested.</div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div> <div id="bloop_sign_1449753531834928896" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">-- <br>Arun</div></div> <br><p class="airmail_on">On 9 December 2015 at 13:19:11, Santosh Srinivas (<a href="mailto:santosh.srinivas@gmail.com">santosh.srinivas@gmail.com</a>) wrote:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>
<title></title>
<div dir="ltr">Hello All,
<div><br></div>
<div>I am sure there is a much more efficient way to do this.
Please advise any suggestions.</div>
<div>For now, I have boot fixed this the crude way :-(</div>
<div><br></div>
<div>
<div>age_brackets <-
c("pop_0:pop_3","pop_4:pop_6","pop_7:pop_9")</div>
<div><br></div>
<div>for (i in age_brackets) {</div>
<div>cmdText <- paste('dt[, paste("",i,sep=""):= rowSums(.SD,
na.rm=TRUE), by=list(origin, race, sex,year, total_pop),
.SDcols=',i,']', sep="")</div>
<div>print(cmdText)</div>
<div>eval(parse(text=cmdText))</div>
<div>}</div>
</div>
<div><br></div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Dec 8, 2015 at 11:13 PM, Santosh
Srinivas <span dir="ltr"><<a href="mailto:santosh.srinivas@gmail.com" target="_blank">santosh.srinivas@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">Hello All,
<div><br></div>
<div>I have a dataset as below with a reproducible example after
that. My actual data has about 100 columns.</div>
<div><br></div>
<div>I want columns that represent the rowSums for sets .. eg.
pop_0_3, pop_4_6, pop_7_9 .. this is sum of population in age
group of 0-3 for example.</div>
<div><br></div>
<div>How can I do that using indexes of the columns?</div>
<div><br></div>
<div>
---------------------------------------------------------------------------------------------------------------------------------------------------------<br>
</div>
<div><br></div>
<div>
<div> origin race sex year total_pop pop_0
pop_1 pop_2 pop_3 pop_4 pop_5
pop_6 pop_7 pop_8 pop_9</div>
<div> 1: 0 0 0 2014
318748017 3971847 3957864 3972081 4003272 4001929 4002977 4132455
4152653 4118628 4105776</div>
<div> 2: 0 0 0 2015
321368864 4000831 3988161 3974109 3986357 4015656 4013264 4013790
4142998 4163270 4129322</div>
<div> 3: 0 0 0 2016
323995528 4029356 4017346 4004585 3988434 3998839 4026967 4024121
4024481 4153686 4174008</div>
<div> 4: 0 0 0 2017
326625791 4057231 4046063 4033932 4019069 4000955 4010232 4037777
4034839 4035311 4164487</div>
<div> 5: 0 0 0 2018
329256465 4083375 4074132 4062816 4048550 4031712 4012371 4021117
4048454 4045696 4046249</div>
<div> 6: 0 0 0 2019
331883986 4107606 4100469 4091055 4077589 4061316 4043229 4023269
4031853 4059256 4056646</div>
<div> 7: 0 0 0 2020
334503458 4128810 4124893 4117546 4105953 4090466 4072931 4054223
4034013 4042721 4070166</div>
<div> 8: 0 0 0 2021
337108968 4145903 4146269 4142090 4132527 4118898 4102128 4083950
4065004 4044832 4053623</div>
<div> 9: 0 0 0 2022
339698079 4159190 4163587 4163657 4157230 4145600 4130675 4113256
4094835 4075940 4055771</div>
<div>10: 0 0 0 2023
342267302 4169856 4177093 4181156 4178958 4170441 4157505 4141921
4124243 4105873 4086972</div>
</div>
<div><br></div>
<div><br></div>
<div>
---------------------------------------------------------------------------------------------------------------------------------------------------------<br>
</div>
<div><br></div>
<div><br></div>
<div>
<div># <a href="https://www.census.gov/population/projections/files/downloadables/NP2014_D1.csv" target="_blank">https://www.census.gov/population/projections/files/downloadables/NP2014_D1.csv</a></div>
<div><br></div>
<div>require("data.table")</div>
<div><br></div>
<div>dt <- structure(list(origin = c(0L, 0L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, </div>
<div>0L), race = c(0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L), sex =
c(0L, </div>
<div>0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L), year = 2014:2023,
total_pop = c(318748017L, </div>
<div>321368864L, 323995528L, 326625791L, 329256465L, 331883986L,
334503458L, </div>
<div>337108968L, 339698079L, 342267302L), pop_0 = c(3971847L,
4000831L, </div>
<div>4029356L, 4057231L, 4083375L, 4107606L, 4128810L, 4145903L,
4159190L, </div>
<div>4169856L), pop_1 = c(3957864L, 3988161L, 4017346L,
4046063L, </div>
<div>4074132L, 4100469L, 4124893L, 4146269L, 4163587L,
4177093L), </div>
<div> pop_2 = c(3972081L, 3974109L, 4004585L,
4033932L, 4062816L, </div>
<div> 4091055L, 4117546L, 4142090L, 4163657L,
4181156L), pop_3 = c(4003272L, </div>
<div> 3986357L, 3988434L, 4019069L, 4048550L,
4077589L, 4105953L, </div>
<div> 4132527L, 4157230L, 4178958L), pop_4 =
c(4001929L, 4015656L, </div>
<div> 3998839L, 4000955L, 4031712L, 4061316L,
4090466L, 4118898L, </div>
<div> 4145600L, 4170441L), pop_5 = c(4002977L,
4013264L, 4026967L, </div>
<div> 4010232L, 4012371L, 4043229L, 4072931L,
4102128L, 4130675L, </div>
<div> 4157505L), pop_6 = c(4132455L, 4013790L,
4024121L, 4037777L, </div>
<div> 4021117L, 4023269L, 4054223L, 4083950L,
4113256L, 4141921L</div>
<div> ), pop_7 = c(4152653L, 4142998L, 4024481L,
4034839L, 4048454L, </div>
<div> 4031853L, 4034013L, 4065004L, 4094835L,
4124243L), pop_8 = c(4118628L, </div>
<div> 4163270L, 4153686L, 4035311L, 4045696L,
4059256L, 4042721L, </div>
<div> 4044832L, 4075940L, 4105873L), pop_9 =
c(4105776L, 4129322L, </div>
<div> 4174008L, 4164487L, 4046249L, 4056646L,
4070166L, 4053623L, </div>
<div> 4055771L, 4086972L)), .Names = c("origin",
"race", "sex", </div>
<div>"year", "total_pop", "pop_0", "pop_1", "pop_2", "pop_3",
"pop_4", </div>
<div>"pop_5", "pop_6", "pop_7", "pop_8", "pop_9"), class =
c("data.table", </div>
<div>"data.frame"), row.names = c(NA, -10L))</div>
</div>
<div><br></div>
<div><br></div>
<div>
---------------------------------------------------------------------------------------------------------------------------------------------------------<br>
</div>
<div><br></div>
<div>Thank you.</div>
<div><span class="HOEnZb"><font color="#888888">Santosh</font></span></div>
</div>
</blockquote>
</div>
<br></div>
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