R：如何用数据框列表替换名称列表？

Question

I want to convert a list of dataframes's names to a list of dataframes.

Example:

datalist <- list("mtcars","swiss","iris")

Then I want to do something like

for(i in 1:length(datalist)) {
 datalist[[i]] <- parse(datalist[[i]])
}

So when I run datalist[[i]] I see the same as this

> mtcars
                     mpg cyl  disp  hp drat    wt  qsec vs am gear carb
Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1

and not

> datalist[[i]]
"mtcars"

Answer 1

mget is the appropriate function. It works on a character vector of object names and returns a list of objects. I use unlist to convert your list to a character vector:

mget(unlist(datalist))

Note that this will not work on the built-in data frames in your example unless (a) you set the inherits option to TRUE like this: mget(unlist(datalist), inherits = TRUE) , or (b) they have already been loaded into the global environment (eg, using data() ).

One advantage of mget compared to other answers proposed here is that the resulting list is created with the names of the objects as the names of the list.

Answer 2

Consider using get :

datalist <- list("mtcars","swiss","iris")

dfList <- lapply(datalist, get)

for(i in 1:length(dfList)) {
  print(head(dfList[[i]]))
}

#                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
# Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
# Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
# Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
# Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
# Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
# Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1

#          Fertility Agriculture Examination Education Catholic Infant.Mortality
# Courtelary        80.2        17.0          15        12     9.96             22.2
# Delemont          83.1        45.1           6         9    84.84             22.2
# Franches-Mnt      92.5        39.7           5         5    93.40             20.2
# Moutier           85.8        36.5          12         7    33.77             20.3
# Neuveville        76.9        43.5          17        15     5.16             20.6
# Porrentruy        76.1        35.3           9         7    90.57             26.6

# Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1          5.1         3.5          1.4         0.2  setosa
# 2          4.9         3.0          1.4         0.2  setosa
# 3          4.7         3.2          1.3         0.2  setosa
# 4          4.6         3.1          1.5         0.2  setosa
# 5          5.0         3.6          1.4         0.2  setosa
# 6          5.4         3.9          1.7         0.4  setosa

Answer 3

Instead of

parse(datalist[[i]])

use:

eval(parse(text = datalist[[i]]))

You need to evaluate the output of parse.