# [R] Extract complete rows by group and maximum

Dimitris Rizopoulos d.rizopoulos at erasmusmc.nl
Thu Apr 28 13:45:23 CEST 2011

```two possibilities are:

f <- factor(DF\$cvd_basestudy, unique(DF\$cvd_basestudy))
ind <- ave(DF\$es_time, f, FUN = function (x) x == max(x))
DF[as.logical(ind), ]

f <- factor(DF\$cvd_basestudy, unique(DF\$cvd_basestudy))
lis <- lapply(split(DF, f), function (d) d[which.max(d\$es_time), ])
do.call(rbind, lis)

with DF <- datares_sinus_variable.

I hope it helps.

Best,
Dimitris

On 4/28/2011 1:31 PM, Sandy Small wrote:
> Hi
>
> I'm trying to extract complete rows from a dataframe by group based on
> the maximum in a column within that group.
> Thus I have a dataframe:
>
> cvd_basestudy ... es_time ...
> _____________
> study1 ... 0.3091667
> study2 ... 0.3091667
> study2 ... 0.2625000
> study3 ... 0.3033333
> study3 ... 0.2625000
> __________
> etc
>
> I can extract the basestudy and the max(es_time) using ddply
> ddply(datares_sinus_variable, .(cvd_basestudy),
> function(x){max(x[['es_time']])})
> or by
> by(datares_sinus_variable\$es_time, datares_sinus_variable\$cvd_basestudy,
> max)
>
> but how do I extract the whole line so that I can get a dataframe with
> all the data for the maximum line?
>
> (dput output from first 5 rows of my actual dataframe follows)
>
> Any help would be much appreciated. Thanks in advance
> Sandy Small
>
> structure(list(cvd_basestudy = c("study1", "study2", "study2",
> "study3", "study3"), ecd_rhythm = structure(c(5L, 5L, 5L, 5L,
> 5L), .Label = c("AF", "FLUTTER", "PACED AF", "SCRAP", "SINUS",
> "UNSURE"), class = "factor"), cvd_frame_mode = structure(c(2L,
> 2L, 2L, 2L, 2L), .Label = c("fixed_time", "variable_time"), class =
> "factor"),
> cvd_part_fmt = structure(c(4L, 4L, 4L, 4L, 4L), .Label = c("first",
> "last", "mid", "whole"), class = "factor"), cvd_prev_fmt =
> structure(c(1L,
> 2L, 1L, 3L, 2L), .Label = c("All", "Best", "Q1", "Q2", "Q3",
> "Q4"), class = "factor"), cvd_cur_fmt = structure(c(5L, 5L,
> 1L, 4L, 4L), .Label = c("All", "Best", "Q1", "Q2", "Q3",
> "Q4"), class = "factor"), ps_pt = c(1, 1, 2, 1, 2), es_pt = c(8,
> 8, 8, 8, 8), ed_pt = c(21, 21, 18, 17, 18), cvd_median_limit = c(1.057,
> 1.057, 1.048, 1.037, 1.05), cvd_average_beat = c(1.06, 1.06,
> 1.05, 1.04, 1.05), limit = c(0.9, 0.9, 0.9, 0.9, 0.9), sstd_mi =
> c(FALSE,
> FALSE, FALSE, FALSE, FALSE), sstd_hbp = c(FALSE, FALSE, FALSE,
> FALSE, FALSE), sstd_ptca = c(FALSE, FALSE, FALSE, FALSE,
> FALSE), sstd_cabg = c(TRUE, TRUE, TRUE, TRUE, TRUE), sstd_norm_perf
> = c(FALSE,
> FALSE, FALSE, FALSE, FALSE), sstd_posnegett = structure(c(NA_integer_,
> NA_integer_, NA_integer_, NA_integer_, NA_integer_), .Label = c("-",
> "+"), class = "factor"), sstd_function = structure(c(NA_integer_,
> NA_integer_, NA_integer_, NA_integer_, NA_integer_), .Label =
> c("MODERATE",
> "NORMAL", "POOR", "VERY POOR"), class = "factor"), cvd_cur_fmt_n = c(3,
> 3, NA, 2, 2), cvd_prev_fmt_n = c(NA, NA, NA, 1, NA), cvd_cur_fmt2 =
> structure(c(3L,
> 3L, 1L, 3L, 3L), .Label = c("All", "Best", "Quartiles"), class =
> "factor"),
> cvd_prev_fmt2 = structure(c(1L, 2L, 1L, 3L, 2L), .Label = c("All",
> "Best", "Quartiles"), class = "factor"), es_time = c(0.309166666666667,
> 0.309166666666667, 0.2625, 0.303333333333333, 0.2625), es_time_err =
> c(0.0441666666666667,
> 0.0441666666666667, 0.04375, 0.0433333333333333, 0.04375),
> ed_time = c(0.574166666666667, 0.574166666666667, 0.4375,
> 0.39, 0.4375)), .Names = c("cvd_basestudy", "ecd_rhythm",
> "cvd_frame_mode", "cvd_part_fmt", "cvd_prev_fmt", "cvd_cur_fmt",
> "ps_pt", "es_pt", "ed_pt", "cvd_median_limit", "cvd_average_beat",
> "limit", "sstd_mi", "sstd_hbp", "sstd_ptca", "sstd_cabg", "sstd_norm_perf",
> "sstd_posnegett", "sstd_function", "cvd_cur_fmt_n", "cvd_prev_fmt_n",
> "cvd_cur_fmt2", "cvd_prev_fmt2", "es_time", "es_time_err", "ed_time"
> ), row.names = c("651", "655", "656", "661", "663"), class = "data.frame")
>
>
> ********************************************************************************************************************
>
>
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--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
Web: http://www.erasmusmc.nl/biostatistiek/

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