在R data.frames中提取具有常数的列 [英] Extracting columns with constant numbers in R data.frames

问题描述

在data.frame DATA中，有些列在称为study.name的第一列的唯一行中是恒定数.例如，列ESL和prof对于Shin.Ellis的所有行都是恒定，对于Trus.Hsu的所有行都是恒定，依此类推.包括Shin.Ellis和Trus.Hsu，有 8 个唯一的study.name行.

In data.frame DATA, I have some columns that are constant numbers across the unique rows of the first column called study.name. For example, columns ESL and prof are constant for all rows of Shin.Ellis and constant for all rows of Trus.Hsu and so on. Including Shin.Ellis and Trus.Hsu, there are 8 unique study.name rows.

但是，如何为这样的常数在唯一的study.name下的所有行仅获取一个数据点(例如，一个用于Shin.Ellis，一个用于Trus.Hsu等).变量? (即，总共 8 行)

BUT after my split.default() call below, how can I obtain only one data-point for all rows under a unique study.name (e.g., one for Shin.Ellis, one for Trus.Hsu etc.) for such constant variables? (i.e., 8 rows overall)

例如，在我的split.default()之后，所有名为ESL的变量都只显示一个唯一的study.name的8行.

For example, after my split.default(), all variables named ESL show only have 8 rows each for a unique study.name.

仅 ESL和prof的我所需的输出在下面进一步显示.

My desired output for ONLY ESL and prof is shown further below.

注意:这是玩具数据.我们首先应该找到常量.一个功能性的答案受到高度赞赏.

NOTE: This is toy data. We first should find constant variables. A functional answer is highly appreciated.

DATA <- read.csv("https://raw.githubusercontent.com/izeh/m/master/irr.csv", h = T)[-(2:3)]
DATA <- setNames(DATA, sub("\\.\\d+$", "", names(DATA)))

tbl <- table(names(DATA))
nm2 <- names(which(tbl==max(tbl)))

L <- split.default(DATA[names(DATA) %in% nm2], names(DATA)[names(DATA) %in% nm2])


## FIRST 8 ROWS of `DATA`:

#    study.name ESL prof scope type   ESL   prof   scope   type
# 1  Shin.Ellis   1    2     1    1     1      2       1      1
# 2  Shin.Ellis   1    2     1    1     1      2       1      1
# 3  Shin.Ellis   1    2     1    2     1      2       1      1
# 4  Shin.Ellis   1    2     1    2     1      2       1      1
# 5  Shin.Ellis   1    2    NA   NA     1      2      NA     NA
# 6  Shin.Ellis   1    2    NA   NA     1      2      NA     NA
# 7    Trus.Hsu   2    2     2    1     2      2       1      1
# 8    Trus.Hsu   2    2    NA   NA     2      2      NA     NA
# .     ...       .    .     .    .     .      .       .      . # `DATA` has 54 rows overall

在split.default()调用后ESL和prof的所需输出:

Desired output for ESL and prof after split.default() call:

# $ESL            ## 8 unique rows for 8 unique `study.name`
#    ESL ESL.1
# 1    1     1
# 7    2     2
# 9    1     1
# 17   1     1
# 23   1     1
# 35   1     1
# 37   2     2
# 49   2     2


# $prof           ## 8 unique rows for 8 unique `study.name`
#    prof prof.1
# 1     2      2
# 7     2      2
# 9     3      3
# 17    2      2
# 23    2      2
# 35    2      2
# 37   NA     NA
# 49    2      2

推荐答案

我们首先可以找到常量列，然后使用lapply对其进行循环，并在每个study.name中仅选择它们的第一行.

We can first find constant columns and then use lapply to loop over them and select only their first row in each study.name.

is_constant <- function(x) length(unique(x)) == 1L 
cols <- names(Filter(all, aggregate(.~study.name, DATA, is_constant)[-1]))

L[cols] <- lapply(L[cols], function(x) 
                      x[ave(x[[1]], DATA$study.name, FUN = seq_along) == 1, ])
L

#$ESL
#   ESL ESL.1
#1    1     1
#7    2     2
#9    1     1
#17   1     1
#23   1     1
#35   1     1
#37   2     2
#49   2     2

#$prof
#   prof prof.1
#1     2      2
#7     2      2
#9     3      3
#17    2      2
#23    2      2
#35    2      2
#37   NA     NA
#49    2      2
#.....

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