问题
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- Reshaping multiple sets of measurement columns (wide format) into single columns (long format) 7 answers
I have an R dataframe that I scraped from the internet using readHTMLTable() in the XML package. The table looks like the following excerpt with multiple variables/columns for population and year. (Note that the years are not duplicated across columns and represent a unique identifier for population.)
year1 pop1 year2 pop2 year3 pop3
1
2 16XX 4675,0 1900 6453,0 1930 9981,2
3 17XX 4739,3 1901 6553,5 1931 ...
4 17XX 4834,0 1902 6684,0 1932
5 180X 4930,0 1903 6818,0 1933
6 180X 5029,0 1904 6955,0 1934
7 181X 5129,0 1905 7094,0 1935
8 181X 5231,9 1906 7234,7 1936
9 182X 5297,0 1907 7329,0 1937
10 182X 5362,0 1908 7422,0 1938
I would like to reorganize the data into just two columns, one for year and one for population that looks like the following:
year pop
1
2 16XX 4675,0
3 17XX 4739,3
4 17XX 4834,0
5 180X 4930,0
6 180X 5029,0
7 181X 5129,0
8 181X 5231,9
9 182X 5297,0
10 182X 5362,0
11 1900 6453,0
12 1901 6553,5
13 1902 6684,0
... ... ...
21 1930 9981,2
22 ...
The values from the variables/columns year2 and year3 are appended below year1, as are the corresponding population values.
I have considered the following:
(1) Looping over the population and year columns (n>2) and adding those values as new observations to year1 and population1 will work, but this seems unnecessarily cumbersome.
(2) I have tried melt as below, but either it cannot handle the id variable split across multiple columns, or I am not implementing it correctly.
df.melt <- melt(df, id=c("year1", "year2",...)
(3) Lastly, I considered pulling out each year column as its own vector, and appending each of those vectors together as here:
year.all <- c(df$year1, df$year2,...)
However, the above returns the following for year.all
[1] 1 2 3 3 4 4 5 5 6 6 7 8 8 9 9 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 1 1 2 ...
rather than this
[1] 16XX 17XX 17XX 180X 180X 181X 181X 182X 182X 1900 1901 1902...
If there is a straightforward way of accomplishing this reorganizing I would love to learn it. Many thanks for the help.
回答1:
If the 'year', 'pop', columns are alternating, we can subset with c(TRUE, FALSE) to get the columns 1, 3, 5,..etc. and c(FALSE, TRUE) to get 2, 4, 6,.. due to the recycling. Then, we unlist the columns and create a new 'data.frame.
df2 <- data.frame(year=unlist(df1[c(TRUE, FALSE)]),
pop=unlist(df1[c(FALSE, TRUE)]))
row.names(df2) <- NULL
head(df2)
# year pop
#1
#2 16XX 4675,0
#3 17XX 4739,3
#4 17XX 4834,0
#5 180X 4930,0
#6 180X 5029,0
Or another option is
library(splitstackshape)
merged.stack(transform(df1, id=1:nrow(df1)), var.stubs=c('year', 'pop'),
sep='var.stubs')[order(.time_1), 3:4, with=FALSE]
data
df1 <- structure(list(year1 = c("", "16XX", "17XX", "17XX", "180X",
"180X", "181X", "181X", "182X", "182X"), pop1 = c("", "4675,0",
"4739,3", "4834,0", "4930,0", "5029,0", "5129,0", "5231,9", "5297,0",
"5362,0"), year2 = c(NA, 1900L, 1901L, 1902L, 1903L, 1904L, 1905L,
1906L, 1907L, 1908L), pop2 = c("", "6453,0", "6553,5", "6684,0",
"6818,0", "6955,0", "7094,0", "7234,7", "7329,0", "7422,0"),
year3 = c(NA, 1930L, 1931L, 1932L, 1933L, 1934L, 1935L, 1936L,
1937L, 1938L), pop3 = c("", "9981,2", "", "", "", "", "",
"", "", "")), .Names = c("year1", "pop1", "year2", "pop2",
"year3", "pop3"), class = "data.frame", row.names = c(NA, -10L))
回答2:
Using the new feature in melt from data.table v1.9.5+:
require(data.table) # v1.9.5+
melt(setDT(df), measure = patterns("^year", "^pop"), value.name = c("year", "pop"))
You can find the rest of the vignettes here.
回答3:
Another option is to use split.default to split the dataframe in a list of dataframes and then bind them together:
lst <- lapply(split.default(df1, sub('.*(\\d)', '\\1', names(df1))),
setNames, c('year','pop'))
do.call(rbind, lst)
which gives the desired result:
year pop 1.1 16XX 4675,0 1.2 17XX 4739,3 1.3 17XX 4834,0 1.4 180X 4930,0 1.5 180X 5029,0 1.6 181X 5129,0 1.7 181X 5231,9 1.8 182X 5297,0 1.9 182X 5362,0 2.1 1900 6453,0 2.2 1901 6553,5 2.3 1902 6684,0 2.4 1903 6818,0 2.5 1904 6955,0 2.6 1905 7094,0 2.7 1906 7234,7 2.8 1907 7329,0 2.9 1908 7422,0 3.1 1930 9981,2 3.2 1931 10583,5 3.3 1932 8671,0 3.4 1933 9118,0 3.5 1934 9625,0 3.6 1935 8097,0 3.7 1936 7984,7 3.8 1937 8729,0 3.9 1938 10462,0
You could also use rbindlist from the data.table package for the last step:
library(data.table)
rbindlist(lst)
Used data:
df1 <- structure(list(year1 = c("16XX", "17XX", "17XX", "180X", "180X", "181X", "181X", "182X", "182X"),
pop1 = c("4675,0", "4739,3", "4834,0", "4930,0", "5029,0", "5129,0", "5231,9", "5297,0", "5362,0"),
year2 = c(1900L, 1901L, 1902L, 1903L, 1904L, 1905L, 1906L, 1907L, 1908L),
pop2 = c("6453,0", "6553,5", "6684,0", "6818,0", "6955,0", "7094,0", "7234,7", "7329,0", "7422,0"),
year3 = c(1930L, 1931L, 1932L, 1933L, 1934L, 1935L, 1936L, 1937L, 1938L),
pop3 = c("9981,2", "10583,5", "8671,0", "9118,0", "9625,0", "8097,0", "7984,7", "8729,0", "10462,0")),
.Names = c("year1", "pop1", "year2", "pop2", "year3", "pop3"), class = "data.frame", row.names = c(NA, -9L))
来源：https://stackoverflow.com/questions/31504735/reshape-a-dataframe-to-long-format-with-multiple-sets-of-measure-columns