如何从csv中读取数据帧名称并在R中的循环中使用它

Question

I have created some 500 data frames in the global environment of R studio and I have the list of all these data frame names in a csv file. I need to collect the no. of observations of each data frames. I know I need to use the nrow(dataset_name) command but is there any way, I can create a loop such that R reads the dataset names from the csv and executes the nrow command?

ps- I am a newbie to R, so plz pardon me if this question is very basic. TIA!

Regards, Brock

Answer 1

Sample Example Below:

 # Creating 3 data frames
 df1=data.frame(a=1:12,b=1:12)   # Number of rows 12
 df2=data.frame(a=1:5,b=1:5)     # Number of rows 5
 df3=data.frame(a=1:20,b=1:20)   # Number of rows 20

 # Storing the created data frames in a list
 df_names=list(df1,df2,df3)

 # Computing the number of rows for each data frame
 for(i in 1:length(df_names)){
 print(nrow(df_names[[i]]))
 }
 # [1] 12
 # [1] 5
 # [1] 20

Note that here the data frames created are all saved in a list, not the dataframe names but the data frames and not in the csv file.

If you have 500 dataframes with you with data frames name as df1,df2,....,df499, df500, you can create list using paste and then you can apply the same above for loop.

df_names=list(paste("df",1:500,sep=""))