在依赖不同子字符串的单独列中创建值

Question

I have the following data frame in R after using melt on some wide-format data:

Condition value
C1SSC     4.5
C2SSC     7.7
TC1SSC    6.0
TC2SSC    7.3
PC1SSC    4.5
PC2SSC    5.7

Each character or substring has a specific meaning (for instance, TC2SSC means a condition where a textured [T] circle [C] was viewed with both eyes [2], and the response 'starting shape' was a circle [SSC]).

What I want to do is generate new variable columns that are dependent on these characters and substrings - one for texture, one for shape and so on. I thought about using grepl or substr , but I'm not sure if these can evaluate specific parts of strings (ie when ascertaining shape, checking the first two characters to see if they contain a 'C').

Ideally, this is what I'd end up with (example for TC2SSC):

Texture    Shape    View    startShape    value
T          Circle   2       Circle        4.5

There are a lot of useful functions, but I'm not sure which is the best to use here. Any advice would be much appreciated.

Answer 1

Here's a straightforward way to approach the problem. Basically, use a pattern with gsub to insert a character after every character (here "_") that you want to "split" and then use strsplit on it. Here's how:

split.df <- data.frame(do.call(rbind, strsplit(gsub("(C|SSC|[0-9]+)", "_\\1_", 
                      dt$Condition), "[_]+")), stringsAsFactors=FALSE)

#   X1 X2 X3  X4
# 1     C  1 SSC
# 2     C  2 SSC
# 3  T  C  1 SSC
# 4  T  C  2 SSC
# 5  P  C  1 SSC
# 6  P  C  2 SSC

Now, the rest is pretty straightforward (change names, convert classes and replace C to circle etc..)

names(split.df) <- c("Texture", "Shape", "View", "startShape")
split.df <- within(split.df, { Shape[Shape == "C"] <- "Circle" 
            View <- as.numeric(View)
            startShape[startShape == "SSC"] <- "Circle"} )
cbind(split.df, value = df$value)

#   Texture  Shape View startShape df$value
# 1         Circle    1     Circle      4.5
# 2         Circle    2     Circle      7.7
# 3       T Circle    1     Circle      6.0
# 4       T Circle    2     Circle      7.3
# 5       P Circle    1     Circle      4.5
# 6       P Circle    2     Circle      5.7